backlight: l4f00242t03: Remove redundant spi_set_drvdata

Driver core sets driver data to NULL upon failure or remove.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>