media: stv090x: Only print tuner lock if get_status is available

The current code doesn't report tuner lock properly if the
tuner get_status callback is not available, as reported by
smatch:
	drivers/media/dvb-frontends/stv090x.c:2220 stv090x_get_coldlock() error: uninitialized symbol 'reg'.

Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>