ARM: dts: mmp2-olpc-xo-1-75: Fix camera I2C node validation

ARM: dts: mmp2-olpc-xo-1-75: Fix camera I2C node validation

mmp2-olpc-xo-1-75.dt.yaml: camera_i2c: $nodename:0:
      'camera_i2c' does not match '^i2c(@.*)?'
  mmp2-olpc-xo-1-75.dt.yaml: camera_i2c: 'sda-gpios' is a required property
  mmp2-olpc-xo-1-75.dt.yaml: camera_i2c: 'scl-gpios' is a required property

The "gpios" property actually was documented as deprecated, but got dropped
in commit 0175ce4a58d6 ("dt-bindings: i2c: Convert i2c-gpio binding to
json-schema"). It's probably best kept forgotten though.

Link: https://lore.kernel.org/r/20200718205019.184927-2-lkundrak@v3.sk
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>