intel_scu_ipc: fix indentation in few places

While here, do couple of amendments:
 - move platform variable to the function where it's used
 - define intel_scu_ipc_check_status() static

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