V4L/DVB (13241): Cleanup redundant tests on unsigned

The variables are unsigned so the test `>= 0' is always true,
the `< 0' test always fails. In these cases the other part of
the test catches wrapped values.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>