drm_hwcomposer: avoid using signed errno on uint32 type

DrmGenericImporter::ConvertHalFormatToDrm() should not return negative values.

 - Use DRM_FORMAT_INVALID instead of -EINVAL
 - Check DrmGenericImporter::ConvertHalFormatToDrm() result value in
   DrmGenericImporter::ImportBuffer()

Signed-off-by: Roman Stratiienko <roman.stratiienko@globallogic.com>
1 job for fix-signed-errno-pr in 2 minutes and 10 seconds (queued for 47 seconds)