[media] as102: add missing viterbi lock

In order to get FE_HAS_SYNC, the viterbi should already be
locked too. So, add the missing FE_HAS_VITERBI lock.

Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

diff --cc drivers/media/dvb-frontends/as102_fe.c
Simple merge