dm-raid: do not include dm-core.h

In commit 4cc96131afce ("dm: move request-based code out to dm-rq.[hc]")
we have a note: "DM targets should _never_ include dm-core.h!". And it
is not used in any DM targets except dm-raid now, so let's remove it
from dm-raid for consistency, also use special helpers instead of
accessing dm_table and mapper_device fields directly. This change is
merely a cleanup and should not affect functionality.

Signed-off-by: Pavel Tikhomirov <[e-mail]>
Reviewed-by: Yu Kuai <[e-mail]>
Signed-off-by: Mikulas Patocka <[e-mail]>

drivers/md/dm-raid.c

···
 #include "raid5.h"
 #include "raid10.h"
 #include "md-bitmap.h"
-#include "dm-core.h"
 
 #include <linux/device-mapper.h>
 
···
 
 	/* Disable/enable discard support on raid set. */
 	configure_discard_support(rs);
-	rs->md.dm_gendisk = ti->table->md->disk;
+	rs->md.dm_gendisk = dm_disk(dm_table_get_md(ti->table));
 
 	mddev_unlock(&rs->md);
 	return 0;