pwm: rz-mtu3: Fix build warning 'num_channel_ios' not described

Fix the below build warning:
warning: Function parameter or member 'num_channel_ios' not described
in 'rz_mtu3_channel_io_map'
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-rz-mtu3.c

@@ -40,7 +40,7 @@
  * struct rz_mtu3_channel_io_map - MTU3 pwm channel map
  *
  * @base_pwm_number: First PWM of a channel
- * @num: number of IOs on the HW channel.
+ * @num_channel_ios: number of IOs on the HW channel.
  */
 struct rz_mtu3_channel_io_map {
 	u8 base_pwm_number;