msm_fb: display: fix frame buffer's ref count leak

This patch clear MDP_MEMORY_ID_TYPE_FB from pipe's
flag so that fput_light() and fget_light() can be applied
to frame buffer evenly at end of pipe operation. Otherwise
there has kernel unable to handle NULL pointer panic caused
by frame buffer's ref count leak.

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