drm/msm: Fix uninitialization and out of bound access issues

Fix uninitialised variables in encoder structure and
out of bound array access in framebuffer init.

Change-Id: I416f5e8708cfb3a4c7aa1fd25c429d9f49cf97e0
Signed-off-by: Shubhashree Dhar <dhar@codeaurora.org>