V4L/DVB (13500): pvrusb2: Fix lingering 16KB FX2 Firmware issues

These are additional fixes to enable proper pvrusb2 support of 16KB
sized FX2 firmware.

Signed-off-by: Mike Isely <isely@pobox.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>