pwm: core: Make of_pwm_get() static

There are no users outside of PWM core of the of_pwm_get().
Make it static.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Link: https://lore.kernel.org/r/20220826172642.16404-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Guenter Roeck <linux@roeck-us.net>