[media] gspca_stv06xx: remove redundant check for err < 0

The comparison of err < 0 is redundant as err has been previously
been assigned to 0 and has not changed.  Remove the redundant check.

Fixes CoverityScan CID#703363 ("Logically dead code")

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