msm: camera: isp: fix for burst frame drop

This change fixes issue in which ISP driver fails to send all
requested frames in burst mode when frame skip is updated runtime. The
root cause is that only frame skip value was modified, but not the
total number of frames driver is waiting for. Now when frame skip
request is received, ISP driver recalculates the total number of
frames to wait and updates frame skip on next reg update.

Change-Id: I7722f5d828e20fcccb0b3b2b8db0276fd28a5bc8
Signed-off-by: c_psiven <psiven@codeaurora.org>