MAINTAINERS: Add qemu-bridge-helper.c to "Network device backends"

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>

MAINTAINERS

@@ -1934,6 +1934,7 @@ M: Jason Wang <jasowang@redhat.com>
 S: Maintained
 F: net/
 F: include/net/
+F: qemu-bridge-helper.c
 T: git https://github.com/jasowang/qemu.git net
 F: qapi/net.json