greybus: lights: remove unnecessary checks

We do not need to check for channels and lights as they can never be
NULL as a big memory array elements.

Signed-off-by: Rui Miguel Silva <rui.silva@linaro.org>
Reported-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>