media: mb86a16: be more resilient if I2C fails on sync

If the I2C read fails while check for sync, there's no point
on doing adjusting the tuner due to a random value that might
be at VIRM var. So, set VIRM to zero, as that makes the caller
for check_sync() to return an error.

Fix those smatch warnings:
	drivers/media/dvb-frontends/mb86a16.c:1460 mb86a16_set_fe() error: uninitialized symbol 'VIRM'.
	drivers/media/dvb-frontends/mb86a16.c:1461 mb86a16_set_fe() error: uninitialized symbol 'VIRM'.

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