] ptp: ocp: remove symlink for second GNSS

Destroy code doesn't remove symlink for ttyGNSS2 device introduced
earlier. Add cleanup code.

Fixes: 71d7e085

 ("ptp: ocp: Add second GNSS device")
Signed-off-by: Vadim Fedorenko <vadfed@fb.com>
Acked-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>