backlight: tosa_bl: Include the right header

The Tosa backlight driver was converted to use GPIO descriptors
in 0b0cb52b
("video: backlight: tosa: Use GPIO lookup table") but
still includes <linux/gpio.h> rather than <linux/gpio/consumer.h>.
Fix it.

Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>