leds: lm36274: cosmetic: rename lm36274_data to chip

Rename this variable so that it is easier to read and easier to write in
80 columns. Also rename variable of this type in lm36274_brightness_set
from led to chip, to be consistent.

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