fuse: remove unused 'inode' parameter in fuse_passthrough_open

The 'inode' parameter in fuse_passthrough_open() is never referenced
in the function implementation.

Signed-off-by: Chunsheng Luo <luochunsheng@ustc.edu>
Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>