msm: camera: Fix for kernel panic

check if buffer instance handle is zero while
getting pcam instance based on instance handle
in msm_mctl_reserve_free_buf function

Change-Id: Id3861c4f29fb4f7fd62ad6de6597e65c7c4f656b
Signed-off-by: manish gotefode <mgote@codeaurora.org>
Merge "msm: camera: Fix for kernel panic" into android-4.4