fuse: create fuse_do_open() helper for CUSE

Create a helper for sending an OPEN request that doesn't need a struct
inode pointer.

Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/fuse/dir.c b/fs/fuse/dir.c
index da87a3d..faa3b2f 100644
--- a/fs/fuse/dir.c
+++ b/fs/fuse/dir.c
@@ -1103,7 +1103,7 @@
 
 static int fuse_dir_open(struct inode *inode, struct file *file)
 {
-	return fuse_open_common(inode, file, 1);
+	return fuse_open_common(inode, file, true);
 }
 
 static int fuse_dir_release(struct inode *inode, struct file *file)