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.de


Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>