V4L/DVB (13495): pvrusb2: Support 16KB FX2 firmware

New FX2 firmware from Hauppauge is no longer 8KB in size - it's 16KB.
This is true for HVR-1950 and HVR-1900 devices.  Without this change,
new pvrusb2 users with that hardware are unable to use the driver
(because the CD shipped with the hardware only has the 16KB firmware).

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