[media] [V3] stv090x: variable 'no_signal' set but not used

Remove variable and ignore return value of stv090x_chk_signal().

Tested by compilation only.

[mchehab@redhat.com: instead of reverting and applying V3,
 applied just the diff patch, for the sake of a cleaner history]
Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Reviewed-by: Manu Abraham <manu@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>