backlight: lp855x: Add dev helper variable to lp855x_probe()

Add a dev local variable to the lp855x_probe(), to replace "&cl->dev"
and "lp->dev" in various places.

Also switch to dev_err_probe() in one case which takes care of not
printing -EPROBE_DEFER errors for us.

This is mostly a preparation for adding ACPI enumeration support which
will use the new "dev" variable more.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20211102225504.18920-2-hdegoede@redhat.com