can: ti_hecc: Fix uninitialized spinlock in probe

In ti_hecc_probe(), the spinlock  priv->mbx_lock is not
inited, causing a spinlock lockup BUG.

Acked-by: Anant Gole <anantgole@ti.com>
Signed-off-by: Abhilash K V <abhilash.kv@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>