disp: msm: fix out-of-bound access and NULL dereference

Fix possible out-of-bound access and NULL pointer
dereference in SDE and PLL driver.

Change-Id: Ic5c34b3b4c3e983413a0351c38206cf3f3ab3b1f
Signed-off-by: Samantha Tran <samtran@codeaurora.org>