can: c_can: Fix hardware raminit function

The function is broken in several ways:

    - The function does not wait for the init to complete.
      That can take quite some microseconds.

    - No protection against being called for two chips at the same
      time. SMP is such a new thing, right?

Clear the start and the init done bit unconditionally and wait for both bits to
be clear.

In the enable path set the init bit and wait for the init done bit.

Add proper locking.

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