fuse: fuse_dev_ioctl_clone() should wait for device file to be initialized

fuse: fuse_dev_ioctl_clone() should wait for device file to be initialized

Use fuse_get_dev() not __fuse_get_dev() on the old fd, since in the case of
synchronous INIT the caller will want to wait for the device file to be
available for cloning, just like I/O wants to wait instead of returning an
error.

Fixes: dfb84c330794 ("fuse: allow synchronous FUSE_INIT")
Cc: stable@vger.kernel.org # v6.18
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>