platform/chrome: cros_ec_proto: Mark outdata as const

The 'outdata' is copied to the data buffer in cros_ec_cmd() before being
sent over to the EC. Mark the argument as const so that callers can pass
const pointers to this function and so that callers know the data won't
be modified.

Cc: Prashant Malani <pmalani@chromium.org>
Signed-off-by: Stephen Boyd <swboyd@chromium.org>
Acked-by: Prashant Malani <pmalani@chromium.org>
Link: https://lore.kernel.org/r/20231003003429.1378109-5-swboyd@chromium.org


Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>