MAINTAINERS: Move usb_storage from DFU to USB

The usb_storage.c is the host-side USB mass storage device support,
it is not the DFU/UMS gadget-side implementation. Fix the entry.

Signed-off-by: Marek Vasut <marex@denx.de>
diff --git a/MAINTAINERS b/MAINTAINERS
index f9f4eed..f0918b5 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -855,7 +855,6 @@
 F:	cmd/usb_*.c
 F:	common/dfu.c
 F:	common/update.c
-F:	common/usb_storage.c
 F:	doc/api/dfu.rst
 F:	doc/usage/dfu.rst
 F:	drivers/dfu/
@@ -1483,6 +1482,7 @@
 F:	drivers/usb/
 F:	common/usb.c
 F:	common/usb_kbd.c
+F:	common/usb_storage.c
 F:	include/usb.h
 
 USB xHCI