Btrfs: Change st_blocksize to 4k

Some programs (python) do rwm cycles at the granularity returned by
stat.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 6e2d036..6d0cd9a 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -2701,7 +2701,7 @@
 {
 	struct inode *inode = dentry->d_inode;
 	generic_fillattr(inode, stat);
-	stat->blksize = 256 * 1024;
+	stat->blksize = PAGE_CACHE_SIZE;
 	return 0;
 }