[MMC] Add (MMC) to entry in MAINTAINERS file

Juha Yrjola suggests that adding the string "MMC" to the
maintainers file entry will make it easier to find.  Add
it to the file.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

MAINTAINERS

@@ -1889,7 +1889,7 @@ L:	linux-kernel@vger.kernel.org
 W:	http://www.atnf.csiro.au/~rgooch/linux/kernel-patches.html
 S:	Maintained
 
-MULTIMEDIA CARD SUBSYSTEM
+MULTIMEDIA CARD (MMC) SUBSYSTEM
 P:	Russell King
 M:	rmk+mmc@arm.linux.org.uk
 S:	Maintained