staging: greybus: pwm: Drop unused member from driver struct

The driver doesn't make use of struct gb_pwm_chip::pwm. So that struct
member can just be dropped.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Reviewed-by: Alex Elder <elder@linaro.org>
Link: https://lore.kernel.org/r/20230714201622.2490792-1-u.kleine-koenig@pengutronix.de


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>