[media] xc5000: properly report i2c write failures

The logic as written would *never* actually return an error condition,
since the loop would run until the counter hit zero but the check was
for a value less than zero.

Signed-off-by: Devin Heitmueller <dheitmueller@kernellabs.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>