can: c_can: fix segfault during rmmod

This patch fixes an oops which occurs during unloading the driver.
unregister_c_can_dev() is doing c_can/d_can module interrupts disable, which
requires module clock enable. c_can/d_can interrupts enable/disable is handled
properly in c_can_start and c_can_stop, so removing from
unregister_c_can_dev().

The problem was triggered by adding runtime PM support to the c_can driver by
this commit:

4cdd34b2 can: c_can: Add runtime PM support to Bosch C_CAN/D_CAN controller

Signed-off-by: AnilKumar Ch <anilkumar@ti.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>