[platform][zynq] fix bug in spiflash erase routine
[platform][zynq] fix bug in spiflash erase routine

Forgot to bump offset counter.

sndnvaps/lk,skabet/lk,littlekernel/lk,hollanderic/lkstuff,hollanderic/lkstuff,sndnvaps/lk,ErikCorryGoogle/lk,nvll/lk,nvll/lk,minglun-tsai/lk,skabet/lk,srodrig1/lk,GCrean/lk,M1cha/lk,GCrean/lk,littlekernel/lk,grub4android/lk,travisg/lk,skabet/lk,hollanderic/lkstuff,hollanderic/lkstuff,travisg/lk,minglun-tsai/lk,travisg/lk,srodrig1/lk,M1cha/lk,ErikCorryGoogle/lk,travisg/lk,grub4android/lk,nvll/lk,M1cha/lk,ErikCorryGoogle/lk,ErikCorryGoogle/lk,skabet/lk,GCrean/lk,srodrig1/lk,srodrig1/lk,sndnvaps/lk,GCrean/lk,GCrean/lk,minglun-tsai/lk,sndnvaps/lk,grub4android/lk,srodrig1/lk,littlekernel/lk,M1cha/lk,nvll/lk,M1cha/lk,minglun-tsai/lk,nvll/lk,sndnvaps/lk,skabet/lk,littlekernel/lk,grub4android/lk,grub4android/lk