pwm: twl-led: Add .owner to struct pwm_ops

Add missing .owner of struct pwm_ops. This prevents the module from being
removed from underneath its users.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Thierry Reding <thierry.reding@avionic-design.de>