msm: camera: Fix continuous streaming for controllable output

Request frame number needs to be decremented when frame is ready.
Otherwise we could decide that there is no frame request while
current frame is on going.

Change-Id: I7a5d13c2a53dfcf36d13300470685a0aea9a749c
Signed-off-by: Konstantin Motov <kmotov@codeaurora.org>