leds: leds-is31fl32xx: Provide missing description for member 'sw_shutdown_func'

Fixes the following W=1 kernel build warning(s):

drivers/leds/leds-is31fl32xx.c:85: warning: Function parameter or member 'sw_shutdown_func' not described in 'is31fl32xx_chipdef'

Cc: Pavel Machek <[e-mail]>
Cc: David Rivshin <[e-mail]>
Cc: [e-mail]
Signed-off-by: Lee Jones <[e-mail]>
Signed-off-by: Pavel Machek <[e-mail]>

drivers/leds/leds-is31fl32xx.c

···
  * @pwm_registers_reversed: : true if PWM registers count down instead of up
  * @led_control_register_base : address of first LED control register (optional)
  * @enable_bits_per_led_control_register: number of LEDs enable bits in each
- * @reset_func:         : pointer to reset function
+ * @reset_func          : pointer to reset function
+ * @sw_shutdown_func    : pointer to software shutdown function
  *
  * For all optional register addresses, the sentinel value %IS31FL32XX_REG_NONE
  * indicates that this chip has no such register.