MAINTAINERS: Update OpenRISC mailing list

The mailing list at librecores.org is being shut down due to
infrastructure issues.  Update the the newly created list on
vger.kernel.org.
Signed-off-by: Stafford Horne <shorne@gmail.com>

MAINTAINERS

@@ -15658,7 +15658,7 @@ OPENRISC ARCHITECTURE
 M:	Jonas Bonn <jonas@southpole.se>
 M:	Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>
 M:	Stafford Horne <shorne@gmail.com>
-L:	openrisc@lists.librecores.org
+L:	linux-openrisc@vger.kernel.org
 S:	Maintained
 W:	http://openrisc.io
 T:	git https://github.com/openrisc/linux.git