platform/chrome: cros_ec_i2c: drop BUG_ON() in cros_ec_pkt_xfer_i2c()

It is overkill to crash the kernel if the given message is oversize.

Drop the BUG_ON() and return -EINVAL instead.

Reviewed-by: Guenter Roeck <groeck@chromium.org>
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>
Link: https://lore.kernel.org/r/20220513044143.1045728-6-tzungbi@kernel.org