MAINTAINERS: Add missing header files to BLOCK LAYER section

The various <linux/blk*.h> header files are part of the Block Layer.
Add them to the corresponding section in the MAINTAINERS file, so
scripts/get_maintainer.pl will pick them up.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

MAINTAINERS

@@ -3205,6 +3205,7 @@ S:	Maintained
 T:	git git://git.kernel.org/pub/scm/linux/kernel/git/axboe/linux-block.git
 F:	block/
 F:	drivers/block/
+F:	include/linux/blk*
 F:	kernel/trace/blktrace.c
 F:	lib/sbitmap.c