V4L/DVB (13496): pvrusb2: Support manual extraction of 16KB FX2 firmware

This pvrusb2 change is in support of an existing feature used to help
identify and locate newer vendor supplied firmware.  This change makes
the feature work for the newer larger firmware size.

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