habanalabs: clear msg_to_cpu_reg to avoid misread after reset

For some ASICs, the f/w reads the msg_to_cpu_reg value after
reset, and for some it doesn't.
Therefore, to be sure f/w doesn't read a wrong value after reset, we
need to clear this register before the reset occurs.

Signed-off-by: Koby Elbaz <kelbaz@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>