platform/x86: intel_scu_ipc: Unify the flow in pwr_reg_rdwr()

platform/x86: intel_scu_ipc: Unify the flow in pwr_reg_rdwr()

Unify the flow in pwr_reg_rdwr() with intel_scu_ipc_dev_command_with_size().
While read buffer is not currently being used by the callers of
pwr_reg_rdwr(), this might change in the future. For the existing code
it's a harmless change because the read data for the write operation
is simply discarded.

Tested-by: Ferry Toth <fntoth@gmail.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20241021133705.2933464-2-andriy.shevchenko@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>