[media] saa7164: Variable set but not used

In function saa7164_api_i2c_read variable regval was set but not used.

Tested by compilation only.

Signed-off-by: Peter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>