MAINTAINERS: add dfu.h and dfu.rst to DFU

include/dfu.h and doc/api/dfu.rst belong to the device firmware update
sub-system. So let's add them to DFU in MAINTAINERS.

Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Acked-by: Lukasz Majewski <lukma@denx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index d1c4a28..9da0459 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -600,8 +600,10 @@
 F:	common/dfu.c
 F:	common/update.c
 F:	common/usb_storage.c
+F:	doc/api/dfu.rst
 F:	drivers/dfu/
 F:	drivers/usb/gadget/
+F:	include/dfu.h
 
 DRIVER MODEL
 M:	Simon Glass <sjg@chromium.org>