msm: camera: Ignore STOP command in snapshot mode

Ignore VFE(Video Front End) STOP command if camera
is in snapshot mode and send STOP_ACK as part of
STOP command processing.

Change-Id: Ib9e6af9c6f19d47a873ece9b9916c5ae262a4bfa
CRs-Fixed: 369336
Signed-off-by: Suresh Vankadara <svankada@codeaurora.org>