pwm: tiehrpwm: Make code comment in .free() more useful

Instead of explaining trivia to everyone who can read C describe the
higher-level effect of setting pc->period_cycles[pwm->hwpwm] to zero.

Fixes: 01b2d4536f02 ("pwm: pwm-tiehrpwm: Fix conflicting channel period setting")
Signed-off-by: Uwe Kleine-König <[e-mail]>
Link: https://lore.kernel.org/r/4c38dd1[e-mail]
Signed-off-by: Uwe Kleine-König <[e-mail]>

drivers/pwm/pwm-tiehrpwm.c

···
 {
 	struct ehrpwm_pwm_chip *pc = to_ehrpwm_pwm_chip(chip);
 
-	/* set period value to zero on free */
+	/* Don't let a pwm without consumer block requests to the other channel */
 	pc->period_cycles[pwm->hwpwm] = 0;
 }