mfd: cros_ec: Drop unneeded MODULE_ALIAS

The MODULE_DEVICE_TABLE already creates proper alias.  Having another
MODULE_ALIAS causes the alias to be duplicated:

  $ modinfo cros_ec_dev.ko

  alias:          platform:cros-ec-dev
  srcversion:     F84A69D2156719A4F717A76
  alias:          platform:cros-ec-dev

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>