msm: mdss: fix NULL pointer dereferencing issues

This change fixes the errors reported in static analysis
of MDSS driver code. These changes include fix for various
potential NULL pointer dereferencing and array index out of
bounds issues in MDP, DSI and PP module of MDSS driver.

Change-Id: I49f65f0b4e5218f9fc90469e9d431a3aec811ee2
Signed-off-by: Jayant Shekhar <jshekhar@codeaurora.org>
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>