trivial: synapticsmst: Correct the GUID for the WD15
trivial: synapticsmst: Correct the GUID for the WD15

The WD15 has a slightly different chip than the TB16/TB18 and this was
not transcribed properly.

vathpela/fwupd,fwupd/fwupd,vathpela/fwupd,hughsie/fwupd,fwupd/fwupd,fwupd/fwupd,vathpela/fwupd,vathpela/fwupd,hughsie/fwupd,hughsie/fwupd,hughsie/fwupd,fwupd/fwupd