drm/msm/dsi-staging: Reduce complexity in code

To increse readibilty, functions of larger length are refactored
based on different logic checks in the function. This change doesn't
change any functionality but only improves code readability.

Change-Id: Id9525e2f24d556b38b5ac66a385d8a05b5bc4401
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>