drm_hwcomposer: Clean up error conditions

Clean up error checking for some failure cases.

BUG=None
TEST=Tested on Qemu+drm_hwcomposer

Change-Id: I98bca1aef09060b5a023375dce564252a6073b96
Signed-off-by: Robert Foss <robert.foss@collabora.com>
1 file changed