[media] tua9001: fix a warning

drivers/media/tuners/tua9001.c:211:5: warning: 'ret' may be used uninitialized in this function [-Wmaybe-uninitialized]

Cc: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>