vfs: mnt_drop_write_file()

new helper (wrapper around mnt_drop_write()) to be used in pair with
mnt_want_write_file().

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/ocfs2/ioctl.c b/fs/ocfs2/ioctl.c
index 892ace2..a6fda3c 100644
--- a/fs/ocfs2/ioctl.c
+++ b/fs/ocfs2/ioctl.c
@@ -911,7 +911,7 @@
 			return status;
 		status = ocfs2_set_inode_attr(inode, flags,
 			OCFS2_FL_MODIFIABLE);
-		mnt_drop_write(filp->f_path.mnt);
+		mnt_drop_write_file(filp);
 		return status;
 	case OCFS2_IOC_RESVSP:
 	case OCFS2_IOC_RESVSP64:
diff --git a/fs/ocfs2/move_extents.c b/fs/ocfs2/move_extents.c
index 1d3bf83..b1e3fce 100644
--- a/fs/ocfs2/move_extents.c
+++ b/fs/ocfs2/move_extents.c
@@ -1145,7 +1145,7 @@
 
 	kfree(context);
 
-	mnt_drop_write(filp->f_path.mnt);
+	mnt_drop_write_file(filp);
 
 	return status;
 }