MAINTAINERS: Add some missing entries for USB related files

USB-related docs and include files should go into the USB
section of the MAINTAINERS file.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-id: 1456392967-20274-2-git-send-email-thuth@redhat.com
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>

MAINTAINERS

@@ -857,6 +857,10 @@ M: Gerd Hoffmann <kraxel@redhat.com>
 S: Maintained
 F: hw/usb/*
 F: tests/usb-*-test.c
+F: docs/usb2.txt
+F: docs/usb-storage.txt
+F: include/hw/usb.h
+F: include/hw/usb/
 
 USB (serial adapter)
 M: Gerd Hoffmann <kraxel@redhat.com>