backlight: pwm_bl: Don't use GPIOF_* with gpiod_get_direction

backlight: pwm_bl: Don't use GPIOF_* with gpiod_get_direction

The documentation was wrong, gpiod_get_direction() returns 0/1 instead
of the GPIOF_* flags. The docs were fixed with commit 94fc73094abe47
("gpio: correct docs about return value of gpiod_get_direction"). Now,
fix this user (until a better, system-wide solution is in place).

Signed-off-by: Wolfram Sang <[email protected]>
Acked-by: Daniel Thompson <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Signed-off-by: Lee Jones <[email protected]>