Fix mutex hang in colord on output removal

Fix mutex hang in colord on output removal

Using the x11 output (maybe with others as well), weston would hang
when closing the output if the colord plugin is enabled.

The hang occurs in mutex lock in the output notifier handler because
the given GMutex value is incorrect.

This is because of a cast error, the type of container should be
"cms_output" and not "cms_colord".

Signed-off-by: Olivier Fourdan <ofourdan@redhat.com>
Reviewed-by: Richard Hughes <richard@hughsie.com>
Reviewed-by: Bryce Harrington <bryce@osg.samsung.com>