MAINTAINERS: add drbd headers

Signed-off-by: Christoph Böhmwalder <christoph.boehmwalder@linbit.com>
Reviewed-by: Joel Colledge <joel.colledge@linbit.com>
Link: https://lore.kernel.org/r/20230113123538.144276-7-christoph.boehmwalder@linbit.comSigned-off-by: Jens Axboe <axboe@kernel.dk>

MAINTAINERS

@@ -6421,6 +6421,7 @@ T:	git git://git.linbit.com/linux-drbd.git
 T:	git git://git.linbit.com/drbd-8.4.git
 F:	Documentation/admin-guide/blockdev/
 F:	drivers/block/drbd/
+F:	include/linux/drbd*
 F:	lib/lru_cache.c
 
 DRIVER COMPONENT FRAMEWORK