pwm: meson: Simplify meson_pwm_cnt_to_ns()

pwm: meson: Simplify meson_pwm_cnt_to_ns()

meson_pwm_cnt_to_ns() uses clock rate got from clk_get_rate(). clk object
is getting from driver's private data thru several steps. Since
meson_pwm_cnt_to_ns() is called several times from a single scope it's
easier to get clock rate once and pass it as parameter.

Signed-off-by: George Stark <gnstark@salutedevices.com>
Link: https://lore.kernel.org/r/20241225105639.1787237-2-gnstark@salutedevices.com
Signed-off-by: Uwe Kleine-König <ukleinek@kernel.org>