intel_scu_ipc: Propagate pointer to struct intel_scu_ipc_dev

As much as possible propagate a pointer to struct intel_scu_ipc_dev.

There is no functional change.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>