dax: use sb_issue_zerout instead of calling dax_clear_sectors

dax_clear_sectors() cannot handle poisoned blocks.  These must be
zeroed using the BIO interface instead.  Convert ext2 and XFS to use
only sb_issue_zerout().

Reviewed-by: Jeff Moyer <jmoyer@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
[vishal: Also remove the dax_clear_sectors function entirely]
Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>

fs/ext2/inode.c

@@ -26,6 +26,7 @@
 #include <linux/highuid.h>
 #include <linux/pagemap.h>
 #include <linux/dax.h>
+#include <linux/blkdev.h>
 #include <linux/quotaops.h>
 #include <linux/writeback.h>
 #include <linux/buffer_head.h>
@@ -737,10 +738,9 @@ static int ext2_get_blocks(struct inode *inode,
 		 * so that it's not found by another thread before it's
 		 * initialised
 		 */
-		err = dax_clear_sectors(inode->i_sb->s_bdev,
-				le32_to_cpu(chain[depth-1].key) <<
-				(inode->i_blkbits - 9),
-				count << inode->i_blkbits);
+		err = sb_issue_zeroout(inode->i_sb,
+				le32_to_cpu(chain[depth-1].key), count,
+				GFP_NOFS);
 		if (err) {
 			mutex_unlock(&ei->truncate_mutex);
 			goto cleanup;