usb: dwc2: add T: line to MAINTAINERS showing Felipe's tree

Starting with v3.18-rc, patches for dwc2 will go through Felipe's
tree. Add a T: line to MAINTAINERS to document this.
Signed-off-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

MAINTAINERS

@@ -2849,6 +2849,7 @@ F:	drivers/platform/x86/dell-wmi.c
 DESIGNWARE USB2 DRD IP DRIVER
 M:	Paul Zimmerman <paulz@synopsys.com>
 L:	linux-usb@vger.kernel.org
+T:	git git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb.git
 S:	Maintained
 F:	drivers/usb/dwc2/