leds: lm3697: cosmetic change: use helper variable, reverse christmas tree

Use helper variable dev instead of always writing &client->dev, or
&priv->client->dev, or even &led->priv->client->dev.

With one more line moved reverse christmas tree is also achieved.

Signed-off-by: Marek Behún <marek.behun@nic.cz>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>