wacomhid: fix allow trunc flag check
wacomhid: fix allow trunc flag check

The size check would always short circuit as
FU_WAC_DEVICE_FEATURE_FLAG_ALLOW_TRUNC == 0
is never true. The error message was thus never
written even if a difference was found.

With this patch we check if ALLOW_TRUNC is set in flags
instead, and only write the error if it is not.

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