staging: pi433: fix CamelCase for maxMinus variables

Fixes checkpatch warnings:

  CHECK: Avoid CamelCase: <maxMinus12>
  CHECK: Avoid CamelCase: <maxMinus24>
  CHECK: Avoid CamelCase: <maxMinus36>
  CHECK: Avoid CamelCase: <maxMinus48>
  CHECK: Avoid CamelCase: <maxMinus6>

Signed-off-by: Valentin Vidic <Valentin.Vidic@CARNet.hr>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>