MAINTAINERS: Add header files to Block Layer Core section

Suggested-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NAlberto Garcia <berto@igalia.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

MAINTAINERS

@@ -785,6 +785,7 @@ S: Supported
 F: block*
 F: block/
 F: hw/block/
+F: include/block/
 F: qemu-img*
 F: qemu-io*
 F: tests/qemu-iotests/