MAINTAINERS: Update PowerPC 4xx entry

Update my email address

Signed-off-by: Josh Boyer <jwboyer@gmail.com>

MAINTAINERS

@@ -3876,7 +3876,7 @@ F:	arch/powerpc/platforms/512x/
 F:	arch/powerpc/platforms/52xx/
 
 LINUX FOR POWERPC EMBEDDED PPC4XX
-M:	Josh Boyer <jwboyer@linux.vnet.ibm.com>
+M:	Josh Boyer <jwboyer@gmail.com>
 M:	Matt Porter <mporter@kernel.crashing.org>
 W:	http://www.penguinppc.org/
 L:	linuxppc-dev@lists.ozlabs.org