platform/x86: intel_scu_ipc: Rearrange init sequence

Device pointer is used as a flag that everything is prepared.
Nevertheless the assignment happened quite before and there is a window
when a caller can get weird results or even crashes since not all fields
are initialized yet.

Rearrange initialization sequence in ->probe() to prepare everything
before use.

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