Linux 4.12 compat: super_setup_bdi_name() - add missing code

This includes code that was mistakenly left out of the 7dae2c8 merge into
0.6.5.10.  Its inclusion fixes a kernel warning on Kubuntu 17.04:

	WARN_ON(sb->s_bdi != &noop_backing_dev_info);

Reviewed-by: Chunwei Chen <david.chen@osnexus.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #6089
Closes #6324
(backported from zfs upstream commit 7dae2c8)
Signed-off-by: Colin Ian King <colin.king@canonical.com>

Author: tonyhutter

include/sys/zfs_vfsops.h

@@ -64,7 +64,6 @@ typedef struct zfs_mntopts {
 
 typedef struct zfs_sb {
 	struct super_block *z_sb;	/* generic super_block */
-	struct backing_dev_info z_bdi;	/* generic backing dev info */
 	struct zfs_sb	*z_parent;	/* parent fs */
 	objset_t	*z_os;		/* objset reference */
 	zfs_mntopts_t	*z_mntopts;	/* passed mount options */

module/zfs/zfs_vfsops.c

@@ -1403,8 +1403,6 @@ zfs_domount(struct super_block *sb, zfs_mntopts_t *zmo, int silent)
 	sb->s_time_gran = 1;
 	sb->s_blocksize = recordsize;
 	sb->s_blocksize_bits = ilog2(recordsize);
-	zsb->z_bdi.ra_pages = 0;
-	sb->s_bdi = &zsb->z_bdi;
 
 	error = -zpl_bdi_setup(sb, "zfs");
 	if (error)