staging: greybus: light: remove unnecessary error check

It is not necessary to check return value of gb_lights_channel_flash_config.
gb_lights_channel_config returns both successful and error value.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>