Revert "drm/msm/mdp5: Add check for kzalloc"

This reverts commit 3975ea6e.

It breaks the Android kernel api and was added only because of a tiny
drm driver bugfix for an issue that can not ever really be hit, so it is
safe to revert.

Bug: 161946584
Change-Id: Iea27669f1c3b23c9fd6b4d0babc79ffb4e882814
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>