ARM: pxa: hx4700: initialize all the struct pwm_lookup members

ARM: pxa: hx4700: initialize all the struct pwm_lookup members

Instead of relying on the .pwm_period_ns member of the pwm-backlight
driver's platform data, the PWM period can be retrieved from the PWM
lookup table.

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Philipp Zabel <philipp.zabel@gmail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>
(cherry picked from commit fcb355063ffb12a834b3ca1383c9beec9285d568)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>