f2fs: recover fallocated space

If a fallocated file is fsynced, we should recover the i_size after sudden
power cut.

Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>
diff --git a/fs/f2fs/file.c b/fs/f2fs/file.c
index d97e5c4..78110da 100644
--- a/fs/f2fs/file.c
+++ b/fs/f2fs/file.c
@@ -682,6 +682,7 @@
 		i_size_read(inode) < new_size) {
 		i_size_write(inode, new_size);
 		mark_inode_dirty(inode);
+		f2fs_write_inode(inode, NULL);
 	}
 
 	return ret;