powerpc: mpc8536ds: Update maintainer

Signed-off-by: York Sun <york.sun@nxp.com>

board/freescale/mpc8536ds/MAINTAINERS

@@ -1,5 +1,5 @@
 MPC8536DS BOARD
-#M:	-
+M:	York Sun <york.sun@nxp.com>
 S:	Maintained
 F:	board/freescale/mpc8536ds/
 F:	include/configs/MPC8536DS.h