platform/x86: intel_scu_ipc: make intel_scu_ipc_pdata_t const

Make these const as they are only used during a copy operation.

Done using Coccinelle.

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