MAINTAINERS: Add git repository for extcon

This patch add git repository url for EXTCON subsystem.
Following git repository is currently used to maintain EXTCON.
- git://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/extcon.git

Signed-off-by: Chanwoo Choi <cw00.choi@samsung.com>

MAINTAINERS

@@ -3328,6 +3328,7 @@ EXTERNAL CONNECTOR SUBSYSTEM (EXTCON)
 M:	MyungJoo Ham <myungjoo.ham@samsung.com>
 M:	Chanwoo Choi <cw00.choi@samsung.com>
 L:	linux-kernel@vger.kernel.org
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/chanwoo/extcon.git
 S:	Maintained
 F:	drivers/extcon/
 F:	Documentation/extcon/