Revert "drm/msm: Replace PTR_RET with PTR_ERR_OR_ZERO"

This reverts commit aff24cd1.

This reversion is happening as a result of disabling the
disp/dpu directory as it will not be used in 4.19 downstream
display driver and these changes are made in the common layer
which affects the downstream driver functionalities. Separate
patches are submitted to revert the upstream driver and
introduce the downstream version of display driver.

Change-Id: I7143ac32c6c5f08efa056d3f7649474410dfcc5e
Signed-off-by: Samantha Tran <samtran@codeaurora.org>