[media] pvrusb2: remove redundant check on cnt > 8

The 2nd check of cnt > 8 is redundant as cnt is already checked
and thresholded to a maximum of 8 a few statements earlier.
Remove this redundant 2nd check.

Detected by CoverityScan, CID#114281 ("Logically dead code")

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>