MAINTAINERS: update Zwane Mwaikambo's e-mail address

Zwane Mwaikambo's @arm.linux.org.uk address no longer works.  In February
2013 he asked for his gmail address to be used instead [1] so let's just
do that.

[1] http://marc.info/?l=linux-kernel&m=136079068903214&w=2

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Russell King <rmk+kernel@arm.linux.org.uk>
Cc: Zwane Mwaikambo <zwanem@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

CREDITS

@@ -2576,7 +2576,7 @@ S: Toronto, Ontario
 S: Canada
 
 N: Zwane Mwaikambo
-E: zwane@arm.linux.org.uk
+E: zwanem@gmail.com
 D: Various driver hacking
 D: Lowlevel x86 kernel hacking
 D: General debugging