fuse: ioctl: translate ENOSYS in outarg

Fuse shouldn't return ENOSYS from its ioctl implementation. If userspace
responds with ENOSYS it should be translated to ENOTTY.

There are two ways to return an error from the IOCTL request:

 - fuse_out_header.error
 - fuse_ioctl_out.result

Commit 02c0cab8 ("fuse: ioctl: translate ENOSYS") already fixed this
issue for the first case, but missed the second case.  This patch fixes the
second case.

Reported-by: Jonathan Katz <jkatz@eitmlabs.org>
Closes: https://lore.kernel.org/all/CALKgVmcC1VUV_gJVq70n--omMJZUb4HSh_FqvLTHgNBc+HCLFQ@mail.gmail.com/


Fixes: 02c0cab8 ("fuse: ioctl: translate ENOSYS")
Cc: <stable@vger.kernel.org>
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>