MAINTAINERS: add me as the maintainer of mpc837xerdb

Signed-off-by: Sinan Akman <sinan@writeme.com>
Cc: Tom Rini <trini@ti.com>

board/freescale/mpc837xerdb/MAINTAINERS

 MPC837XERDB BOARD
-#M:	Joe D'Abbraccio <ljd015@freescale.com>
-S:	Orphan (since 2014-06)
+M:	Sinan Akman <sinan@writeme.com>
+S:	Maintained
 F:	board/freescale/mpc837xerdb/
 F:	include/configs/MPC837XERDB.h
 F:	configs/MPC837XERDB_defconfig