msm_fb: dsiplay: fix frame buffer f_count leak

Frame buffer maintains a reference count (f_count) which increased
by fget() and decreased by fput(). overlay play will apply
fget() to frame buffer if it was the soruce buffer and fput()
will be applied to it after pipe commit done. However there has
extra fput() apply to frame buffer at the time pipe is freed.
This patch fix the problem by  clear MDP_MEMORY_ID_TYPE_FB from
pipe's flags to avoid extra fput() applying to frame buffer.

CRs-fixed: 411394
Change-Id: Ib2b72e6277480b5ace23cda554be485d9d477b3d
Signed-off-by: Kuogee Hsieh <khsieh@codeaurora.org>
Signed-off-by: Siddhartha Agrawal <agrawals@codeaurora.org>