um: Add arch/x86/um to MAINTAINERS

Signed-off-by: Richard Weinberger <richard@nod.at>

Author: richardweinberger

MAINTAINERS

@@ -7305,6 +7305,7 @@ W:	http://user-mode-linux.sourceforge.net
 S:	Maintained
 F:	Documentation/virtual/uml/
 F:	arch/um/
+F:	arch/x86/um/
 F:	fs/hostfs/
 F:	fs/hppfs/