block: Get rid of blk_get_backing_dev_info()

blk_get_backing_dev_info() is now a simple dereference. Remove that
function and simplify some code around that.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
index efb6ca9..c52a48c 100644
--- a/include/linux/backing-dev.h
+++ b/include/linux/backing-dev.h
@@ -191,7 +191,7 @@
 	sb = inode->i_sb;
 #ifdef CONFIG_BLOCK
 	if (sb_is_blkdev_sb(sb))
-		return blk_get_backing_dev_info(I_BDEV(inode));
+		return I_BDEV(inode)->bd_bdi;
 #endif
 	return sb->s_bdi;
 }