MAINTAINERS: update ARM/BCMRING MTD NAND DRIVER file patterns

Signed-off-by: Joe Perches <joe@perches.com>
Cc: Leo Chen <leochen@broadcom.com>
Cc: Scott Branden <sbranden@broadcom.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>