pwm: starfive: Fix incompatible pointer types

pwm: starfive: Fix incompatible pointer types

Fix starfive_pwm_ptc_get_state func and get_state pointer func and
return types not matching. In the current kernel version, get_status
does not use return value, so no problem. Fix return type to void.

  drivers/pwm/pwm-starfive-ptc.c:152:15: error: initialization from incompatible pointer type [-Werror=incompatible-pointer-types]
    .get_state = starfive_pwm_ptc_get_state,
               ^~~~~~~~~~~~~~~~~~~~~~~~~~

Change-Id: Ifd9fb81ead2b174d138dcad60f464e484074aac4
Signed-off-by: Hoegeun Kwon <hoegeun.kwon@samsung.com>