When dev->driver->master_set() failed ioctl call return 0
but the caller is not the DRM-Master because file_priv->is_master = 0.
Fix that by returning to ioctl caller the driver master_set error code.
Signed-off-by: Benjamin Gaignard <benjamin.gaignard@linaro.org>
Signed-off-by: Dave Airlie <airlied@redhat.com>