platform/chrome: cros_ec_debugfs: Remove dev_warn when console log is not supported

platform/chrome: cros_ec_debugfs: Remove dev_warn when console log is not supported

If the debugfs interface is enabled, every time a CrOS device is
instantiated a warning like this can appear for every probed device.

 "device does not support reading the console log"

The warning message adds nothing, rather it is source of confusion as
this is expected on some cases. For example, on Samus, that has a
cros-ec and a cros-pd instance the message appears twice, and I suspect
this will happen also on those devices that has a non-standard EC.

If the command is not supported just return silently and don't print the
warning, otherwise the code will already print an error.

Signed-off-by: Enric Balletbo i Serra <enric.balletbo@collabora.com>
Reviewed-by: Guenter Roeck <groeck@chromium.org>