can: kvaser_pciefd: kvaser_pciefd_pwm_stop(): remove unnecessary code when setting pwm duty cycle to zero

To set the duty cycle to zero (i.e. pwm_stop), the trigger value shall
be equal to the top value.

This is achieved by reading the value of the top bit field from the pwm
register and then writing back this value to the trigger and top bit
fields.

Addresses-Coverity: ("Logically dead code")
Reported-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NChrister Beskow <chbe@kvaser.com>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>