drm_hwcomposer: Fix missing definition build error on P and earlier

DRM_FORMAT_INVALID was introduced after libdrm-2.4.94, and does not exists in
Android-P and earlier.

Fixes: f63726ca ("drm_hwcomposer: avoid using signed errno on uint32 type")
Signed-off-by: Roman Stratiienko roman.stratiienko@globallogic.com