V4L/DVB (6301): pvrusb: Update DEBUGIFC sysfs to kernel 2.6.13+

The prototypes for the show and store methods of a device_attribute changed in
kernel 2.6.13, but the code in pvrusb2 was never updated.  I guess the
DEBUGIFC stuff isn't used much....

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>