autofs: switch to __vfs_write()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/autofs4/autofs_i.h b/fs/autofs4/autofs_i.h
index 8e98cf9..d10e619 100644
--- a/fs/autofs4/autofs_i.h
+++ b/fs/autofs4/autofs_i.h
@@ -213,7 +213,7 @@
 
 static inline int autofs_prepare_pipe(struct file *pipe)
 {
-	if (!pipe->f_op->write)
+	if (!(pipe->f_mode & FMODE_CAN_WRITE))
 		return -EINVAL;
 	if (!S_ISFIFO(file_inode(pipe)->i_mode))
 		return -EINVAL;