can: kvaser_pciefd: the PWM generator is running at the bus frequency of the system.

The system clock frequency for the bus connected to the PCIe controller
shall be used when calculating the frequency of the PWM, not the CAN
system clock frequency.

Signed-off-by: Christer Beskow <chbe@kvaser.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>