MAINTAINERS: Add an entry for hw/core/null-machine.c

The "Machine core" section sounds like a good match for this file.
Signed-off-by: NThomas Huth <thuth@redhat.com>
Message-Id: <1485150895-19753-1-git-send-email-thuth@redhat.com>
Reviewed-by: NMarcel Apfelbaum <marcel@redhat.com>
Signed-off-by: NEduardo Habkost <ehabkost@redhat.com>

MAINTAINERS

@@ -813,6 +813,7 @@ M: Eduardo Habkost <ehabkost@redhat.com>
 M: Marcel Apfelbaum <marcel@redhat.com>
 S: Supported
 F: hw/core/machine.c
+F: hw/core/null-machine.c
 F: include/hw/boards.h
 
 Xtensa Machines