MAINTAINERS: add tree entry for USB Serial

Add tree entry for USB Serial.

Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/MAINTAINERS b/MAINTAINERS
index b3e9395..94e97a5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -12267,6 +12267,7 @@
 USB SERIAL SUBSYSTEM
 M:	Johan Hovold <johan@kernel.org>
 L:	linux-usb@vger.kernel.org
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial.git
 S:	Maintained
 F:	Documentation/usb/usb-serial.txt
 F:	drivers/usb/serial/