drm/msm/dsi-staging: Allocate correct size of memory

Allocate memory for array using number of bytes rather than number of
elements to avoid out of bounds access to the array while
writing to it.

Change-Id: I5872d180b60f172201a0a0b77b55d518a4464f1f
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>