ptp: ocp: Rename output selector 'GNSS' to 'GNSS1'

As there are may be 2 GNSS outputs, rename the first one for clarity.
This also works around a parsing issue when specifying selectors.

Signed-off-by: Jonathan Lemon <jonathan.lemon@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>