MAINTAINERS: add myself as bootdevice.c maintainer

bootdevice.c was created by me, and I wrote most of
the code in this file. And now I can maintain it,
I'd hope nobody object this.

Cc: Gerd Hoffmann <kraxel@redhat.com>
Signed-off-by: NGonglei <arei.gonglei@huawei.com>
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>

MAINTAINERS

@@ -1078,3 +1078,8 @@ M: Chrysostomos Nanakos <cnanakos@grnet.gr>
 M: Chrysostomos Nanakos <chris@include.gr>
 S: Maintained
 F: block/archipelago.c
+
+Bootdevice
+M: Gonglei <arei.gonglei@huawei.com>
+S: Maintained
+F: bootdevice.c