MAINTAINERS: add tree link for fastboot

Fastboot patches go through the u-boot-dfu tree.

Add a link in the maintainers file for it.

Link: https://lore.kernel.org/r/20240516-gadget-maintainer-v2-1-23cc916df434@baylibre.com


Signed-off-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>

MAINTAINERS

@@ -1118,6 +1118,7 @@ F:	test/py/tests/test_event_dump.py
 FASTBOOT
 M:	Mattijs Korpershoek <mkorpershoek@baylibre.com>
 S:	Maintained
+T:	git https://source.denx.de/u-boot/custodians/u-boot-dfu.git
 F:	cmd/fastboot.c
 F:	doc/android/fastboot*.rst
 F:	include/fastboot.h