pwm: Fix out-of-bounds access in of_pwm_single_xlate()

With args->args_count == 2 args->args[2] is not defined. Actually the
flags are contained in args->args[1].

Fixes: 3ab7b6ac ("pwm: Introduce single-PWM of_xlate function")
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/243908750d306e018a3d4bf2eb745d53ab50f663.1704835845.git.u.kleine-koenig@pengutronix.deSigned-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

drivers/pwm/core.c

@@ -152,7 +152,7 @@ of_pwm_single_xlate(struct pwm_chip *chip, const struct of_phandle_args *args)
 	pwm->args.period = args->args[0];
 	pwm->args.polarity = PWM_POLARITY_NORMAL;
 
-	if (args->args_count == 2 && args->args[2] & PWM_POLARITY_INVERTED)
+	if (args->args_count == 2 && args->args[1] & PWM_POLARITY_INVERTED)
 		pwm->args.polarity = PWM_POLARITY_INVERSED;
 
 	return pwm;