can: c_can: Wait for CONTROL_INIT to be cleared

According to the documentation the CPU must wait for CONTROL_INIT to
be cleared before writing to the baudrate registers.

Signed-off-by: Benedikt Spranger <b.spranger@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>