ramips: gpio-ralink: use ngpios, not ralink,num-gpios

ramips: gpio-ralink: use ngpios, not ralink,num-gpios

DTS properties that match *-gpios are treated specially.

Use ngpios instead, as most GPIO drivers upstream do.

Fixes 5.10 DTS errors such as:
  OF: /palmbus@300000/gpio@600: could not find phandle

Fixes DTC warnings such as:
  Warning (gpios_property): /palmbus@300000/gpio@600:ralink,num-gpios:
  Could not get phandle node for (cell 0)

Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>
Cc: Daniel Golle <daniel@makrotopia.org>