pwm: Update kernel doc for struct pwm_chip

Commit c572f3b9c8b7 ("pwm: Replace PWM chip unique base by unique ID")
changed the members of struct pwm_chip, but failed to update the
documentation accordingly. Catch up and document the new member and drop
description for the two removed ones.
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

include/linux/pwm.h

@@ -281,11 +281,10 @@ struct pwm_ops {
  * @dev: device providing the PWMs
  * @ops: callbacks for this PWM controller
  * @owner: module providing this chip
- * @base: number of first PWM controlled by this chip
+ * @id: unique number of this PWM chip
  * @npwm: number of PWMs controlled by this chip
  * @of_xlate: request a PWM device given a device tree PWM specifier
  * @of_pwm_n_cells: number of cells expected in the device tree PWM specifier
- * @list: list node for internal use
  * @pwms: array of PWM devices allocated by the framework
  */
 struct pwm_chip {