[media] tda18212: round IF frequency to close hardware value

Chip configures IF frequency resolution of 50 kHz. Round it nearest.
Off-by 50 kHz is almost nothing in real life...

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

diff --cc drivers/media/common/tuners/tda18212.c
Simple merge