Fix usb serial RX bug
Fix usb serial RX bug

USBCDC::readEP already already called readStart, so we should not call
it here.

Signed-off-by: Paul Brook <a027184a55211cd23e3f3094f1fdc728df5e0500@nowt.org>

pbrook/mbed,netzimme/mbed-os,FranklyDev/mbed,HeadsUpDisplayInc/mbed,JasonHow44/mbed,cvtsi2sd/mbed-os,jpbrucker/mbed,jrjang/mbed,cvtsi2sd/mbed-os,ban4jp/mbed,c1728p9/mbed-os,Sweet-Peas/mbed,al177/mbed,c1728p9/mbed-os,karsev/mbed-os,JasonHow44/mbed,j-greffe/mbed-os,bentwire/mbed,jpbrucker/mbed,ARM-software/mbed-beetle,Willem23/mbed,ban4jp/mbed,xcrespo/mbed,bcostm/mbed-os,nRFMesh/mbed-os,karsev/mbed-os,kpurusho/mbed,iriark01/mbed-drivers,wodji/mbed,monkiineko/mbed-os,svastm/mbed,nabilbendafi/mbed,maximmbed/mbed,al177/mbed,masaohamanaka/mbed,jeremybrodt/mbed,Tiryoh/mbed,mikaleppanen/mbed-os,rgrover/mbed,Tiryoh/mbed,fvincenzo/mbed-os,mazimkhan/mbed-os,tung7970/mbed-os,logost/mbed,cvtsi2sd/mbed-os,kpurusho/mbed,c1728p9/mbed-os,mikaleppanen/mbed-os,radhika-raghavendran/mbed-os5.1-onsemi,catiedev/mbed-os,screamerbg/mbed,masaohamanaka/mbed,andreaslarssonublox/mbed,Willem23/mbed,mikaleppanen/mbed-os,jferreir/mbed,adustm/mbed,jrjang/mbed,theotherjimmy/mbed,pedromes/mbed,fanghuaqi/mbed,arostm/mbed-os,jrjang/mbed,netzimme/mbed-os,EmuxEvans/mbed,betzw/mbed-os,mmorenobarm/mbed-os,larks/mbed,kl-cruz/mbed-os,svogl/mbed-os,pi19404/mbed,autopulated/mbed,maximmbed/mbed,NitinBhaskar/mbed,radhika-raghavendran/mbed-os5.1-onsemi,sam-geek/mbed,bikeNomad/mbed,GustavWi/mbed,jrjang/mbed,Sweet-Peas/mbed,jamesadevine/mbed,masaohamanaka/mbed,ARM-software/mbed-beetle,Marcomissyou/mbed,kjbracey-arm/mbed,rosterloh/mbed,fpiot/mbed-ats,Shengliang/mbed,svogl/mbed-os,karsev/mbed-os,bikeNomad/mbed,bentwire/mbed,Shengliang/mbed,jamesadevine/mbed,bikeNomad/mbed,pi19404/mbed,NXPmicro/mbed,tung7970/mbed-os,arostm/mbed-os,bcostm/mbed-os,netzimme/mbed-os,wodji/mbed,screamerbg/mbed,cvtsi2sd/mbed-os,Willem23/mbed,pedromes/mbed,Timmmm/mbed,jamesadevine/mbed,betzw/mbed-os,svastm/mbed,Tiryoh/mbed,Tiryoh/mbed,YarivCol/mbed-os,mmorenobarm/mbed-os,pbrook/mbed,naves-thiago/mbed-midi,nvlsianpu/mbed,kpurusho/mbed,brstew/MBED-BUILD,andreaslarssonublox/mbed,RonEld/mbed,j-greffe/mbed-os,Shengliang/mbed,NXPmicro/mbed,mikaleppanen/mbed-os,struempelix/mbed,rosterloh/mbed,pedromes/mbed,jeremybrodt/mbed,netzimme/mbed-os,pi19404/mbed,Sweet-Peas/mbed,nRFMesh/mbed-os,xcrespo/mbed,CalSol/mbed,bulislaw/mbed-os,monkiineko/mbed-os,theotherjimmy/mbed,hwfwgrp/mbed,sam-geek/mbed,karsev/mbed-os,jpbrucker/mbed,radhika-raghavendran/mbed-os5.1-onsemi,radhika-raghavendran/mbed-os5.1-onsemi,sam-geek/mbed,andreaslarssonublox/mbed,EmuxEvans/mbed,Shengliang/mbed,brstew/MBED-BUILD,logost/mbed,sg-/mbed-drivers,andcor02/mbed-os,jeremybrodt/mbed,rgrover/mbed,ban4jp/mbed,FranklyDev/mbed,andcor02/mbed-os,DanKupiniak/mbed,al177/mbed,jrjang/mbed,HeadsUpDisplayInc/mbed,mmorenobarm/mbed-os,fahhem/mbed-os,GustavWi/mbed,adustm/mbed,larks/mbed,xcrespo/mbed,theotherjimmy/mbed,K4zuki/mbed,Archcady/mbed-os,Marcomissyou/mbed,devanlai/mbed,al177/mbed,autopulated/mbed,infinnovation/mbed-os,screamerbg/mbed,hwfwgrp/mbed,mikaleppanen/mbed-os,dbestm/mbed,sam-geek/mbed,nRFMesh/mbed-os,CalSol/mbed,NXPmicro/mbed,getopenmono/mbed,RonEld/mbed,Archcady/mbed-os,fvincenzo/mbed-os,adamgreen/mbed,andreaslarssonublox/mbed,rosterloh/mbed,screamerbg/mbed,NitinBhaskar/mbed,RonEld/mbed,FranklyDev/mbed,wodji/mbed,rgrover/mbed,NXPmicro/mbed,devanlai/mbed,mbedmicro/mbed,bcostm/mbed-os,mazimkhan/mbed-os,maximmbed/mbed,NitinBhaskar/mbed,svastm/mbed,Marcomissyou/mbed,Willem23/mbed,kjbracey-arm/mbed,fvincenzo/mbed-os,svogl/mbed-os,jferreir/mbed,rosterloh/mbed,FranklyDev/mbed,catiedev/mbed-os,cvtsi2sd/mbed-os,jamesadevine/mbed,logost/mbed,getopenmono/mbed,Shengliang/mbed,Sweet-Peas/mbed,Timmmm/mbed,nabilbendafi/mbed,screamerbg/mbed,jferreir/mbed,jferreir/mbed,NXPmicro/mbed,monkiineko/mbed-os,theotherjimmy/mbed,bentwire/mbed,rgrover/mbed,nvlsianpu/mbed,mnlipp/mbed,mnlipp/mbed,brstew/MBED-BUILD,pbrook/mbed,al177/mbed,HeadsUpDisplayInc/mbed,mnlipp/mbed,infinnovation/mbed-os,fanghuaqi/mbed,radhika-raghavendran/mbed-os5.1-onsemi,j-greffe/mbed-os,fahhem/mbed-os,logost/mbed,CalSol/mbed,kpurusho/mbed,bentwire/mbed,hwfwgrp/mbed,andcor02/mbed-os,pradeep-gr/mbed-os5-onsemi,HeadsUpDisplayInc/mbed,tung7970/mbed-os-1,xcrespo/mbed,K4zuki/mbed,nvlsianpu/mbed,pedromes/mbed,naves-thiago/mbed-midi,xcrespo/mbed,EmuxEvans/mbed,naves-thiago/mbed-midi,jferreir/mbed,JasonHow44/mbed,struempelix/mbed,mnlipp/mbed,andcor02/mbed-os,infinnovation/mbed-os,kl-cruz/mbed-os,struempelix/mbed,CalSol/mbed,tung7970/mbed-os-1,mikaleppanen/mbed-os,alertby/mbed,logost/mbed,c1728p9/mbed-os,infinnovation/mbed-os,pedromes/mbed,DanKupiniak/mbed,YarivCol/mbed-os,CalSol/mbed,radhika-raghavendran/mbed-os5.1-onsemi,tung7970/mbed-os-1,sam-geek/mbed,svogl/mbed-os,devanlai/mbed,adamgreen/mbed,fpiot/mbed-ats,autopulated/mbed,devanlai/mbed,kl-cruz/mbed-os,pradeep-gr/mbed-os5-onsemi,ban4jp/mbed,mmorenobarm/mbed-os,andcor02/mbed-os,bulislaw/mbed-os,pradeep-gr/mbed-os5-onsemi,kl-cruz/mbed-os,mnlipp/mbed,jamesadevine/mbed,RonEld/mbed,dbestm/mbed,bulislaw/mbed-os,EmuxEvans/mbed,fpiot/mbed-ats,andreaslarssonublox/mbed,pradeep-gr/mbed-os5-onsemi,tung7970/mbed-os,fahhem/mbed-os,Archcady/mbed-os,hwfwgrp/mbed,jamesadevine/mbed,logost/mbed,RonEld/mbed,mbedmicro/mbed,DanKupiniak/mbed,monkiineko/mbed-os,maximmbed/mbed,larks/mbed,naves-thiago/mbed-midi,Timmmm/mbed,ryankurte/mbed-os,DanKupiniak/mbed,mazimkhan/mbed-os,ryankurte/mbed-os,nRFMesh/mbed-os,NitinBhaskar/mbed,ryankurte/mbed-os,K4zuki/mbed,getopenmono/mbed,kjbracey-arm/mbed,ryankurte/mbed-os,autopulated/mbed,Archcady/mbed-os,karsev/mbed-os,fpiot/mbed-ats,Timmmm/mbed,geky/mbed,fahhem/mbed-os,mbedmicro/mbed,geky/mbed,JasonHow44/mbed,mazimkhan/mbed-os,fpiot/mbed-ats,fvincenzo/mbed-os,NXPmicro/mbed,cvtsi2sd/mbed-os,HeadsUpDisplayInc/mbed,dbestm/mbed,iriark01/mbed-drivers,fanghuaqi/mbed,jpbrucker/mbed,pradeep-gr/mbed-os5-onsemi,Shengliang/mbed,ARM-software/mbed-beetle,Archcady/mbed-os,al177/mbed,ARM-software/mbed-beetle,nabilbendafi/mbed,brstew/MBED-BUILD,tung7970/mbed-os-1,struempelix/mbed,pi19404/mbed,bulislaw/mbed-os,RonEld/mbed,fvincenzo/mbed-os,masaohamanaka/mbed,pradeep-gr/mbed-os5-onsemi,j-greffe/mbed-os,svogl/mbed-os,bentwire/mbed,bcostm/mbed-os,fanghuaqi/mbed,sg-/mbed-drivers,YarivCol/mbed-os,autopulated/mbed,pbrook/mbed,JasonHow44/mbed,YarivCol/mbed-os,jeremybrodt/mbed,YarivCol/mbed-os,mbedmicro/mbed,mnlipp/mbed,betzw/mbed-os,betzw/mbed-os,bremoran/mbed-drivers,catiedev/mbed-os,rosterloh/mbed,getopenmono/mbed,Tiryoh/mbed,tung7970/mbed-os,xcrespo/mbed,kjbracey-arm/mbed,geky/mbed,dbestm/mbed,K4zuki/mbed,adamgreen/mbed,GustavWi/mbed,struempelix/mbed,wodji/mbed,geky/mbed,adustm/mbed,theotherjimmy/mbed,devanlai/mbed,Willem23/mbed,ban4jp/mbed,Tiryoh/mbed,YarivCol/mbed-os,tung7970/mbed-os-1,naves-thiago/mbed-midi,nabilbendafi/mbed,K4zuki/mbed,devanlai/mbed,jeremybrodt/mbed,theotherjimmy/mbed,dbestm/mbed,Sweet-Peas/mbed,fanghuaqi/mbed,wodji/mbed,0xc0170/mbed-drivers,0xc0170/mbed-drivers,netzimme/mbed-os,masaohamanaka/mbed,GustavWi/mbed,svastm/mbed,mazimkhan/mbed-os,adamgreen/mbed,mazimkhan/mbed-os,bcostm/mbed-os,larks/mbed,EmuxEvans/mbed,netzimme/mbed-os,jrjang/mbed,ryankurte/mbed-os,karsev/mbed-os,catiedev/mbed-os,jferreir/mbed,c1728p9/mbed-os,JasonHow44/mbed,larks/mbed,ban4jp/mbed,brstew/MBED-BUILD,K4zuki/mbed,Marcomissyou/mbed,autopulated/mbed,andcor02/mbed-os,Archcady/mbed-os,adamgreen/mbed,alertby/mbed,Timmmm/mbed,nvlsianpu/mbed,naves-thiago/mbed-midi,dbestm/mbed,nRFMesh/mbed-os,Marcomissyou/mbed,arostm/mbed-os,NitinBhaskar/mbed,betzw/mbed-os,arostm/mbed-os,svastm/mbed,c1728p9/mbed-os,fpiot/mbed-ats,brstew/MBED-BUILD,pedromes/mbed,catiedev/mbed-os,pi19404/mbed,kl-cruz/mbed-os,svogl/mbed-os,adustm/mbed,mmorenobarm/mbed-os,infinnovation/mbed-os,fahhem/mbed-os,nvlsianpu/mbed,adustm/mbed,Timmmm/mbed,EmuxEvans/mbed,alertby/mbed,getopenmono/mbed,j-greffe/mbed-os,pi19404/mbed,rgrover/mbed,pbrook/mbed,bulislaw/mbed-os,arostm/mbed-os,HeadsUpDisplayInc/mbed,pbrook/mbed,hwfwgrp/mbed,infinnovation/mbed-os,Marcomissyou/mbed,tung7970/mbed-os,nabilbendafi/mbed,alertby/mbed,alertby/mbed,masaohamanaka/mbed,wodji/mbed,adamgreen/mbed,j-greffe/mbed-os,FranklyDev/mbed,monkiineko/mbed-os,catiedev/mbed-os,mmorenobarm/mbed-os,rosterloh/mbed,bentwire/mbed,maximmbed/mbed,ryankurte/mbed-os,jpbrucker/mbed,bikeNomad/mbed,geky/mbed,screamerbg/mbed,hwfwgrp/mbed,GustavWi/mbed,struempelix/mbed,maximmbed/mbed,nabilbendafi/mbed,CalSol/mbed,kpurusho/mbed,bremoran/mbed-drivers,nRFMesh/mbed-os,bcostm/mbed-os,bikeNomad/mbed,kpurusho/mbed,arostm/mbed-os,adustm/mbed,mbedmicro/mbed,nvlsianpu/mbed,bulislaw/mbed-os,alertby/mbed,Sweet-Peas/mbed,fahhem/mbed-os,getopenmono/mbed,monkiineko/mbed-os,betzw/mbed-os,jpbrucker/mbed,larks/mbed,kl-cruz/mbed-os