msm: jpeg: Unvote the bus soon after encoding done.

Perform bus voting at start-encoding ioctl call and
un-vote right after the encoding is done and before
sending the encoding-done event to userspace
to ensure honest bus voting by jpeg.

Change-Id: I8ae10e3d1e0ad4e62a0120a11b2f20ee6d70b070
Signed-off-by: Sunid Wilson <sunidw@codeaurora.org>