gbm: return appropriate error when queryImage() fails

gbm: return appropriate error when queryImage() fails

Change gbm_dri_bo_get_fd to check the return value of queryImage and
return -1 (an invalid file descriptor) if an error occurs.

Update the comment for gbm_bo_get_fd to return -1, since (apart from the
above) we've already return -1 on error.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Nicholas Bishop <nbishop@neverware.com>
Reviewed-by: Eric Engestrom <eric.engestrom@imgtec.com> (v1)
[Emil Velikov: Split from larger patch, polish coding style, cc stable]
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>