platform/x86: intel_scu_ipcutil: Make scu static

The variable is only used internally and has no external users,
so it should me made static.

Compile-tested only.
Reviewed-by: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Reviewed-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Link: https://lore.kernel.org/r/20240223163901.13504-3-W_Armin@gmx.deSigned-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>

drivers/platform/x86/intel_scu_ipcutil.c

@@ -22,7 +22,7 @@
 
 static int major;
 
-struct intel_scu_ipc_dev *scu;
+static struct intel_scu_ipc_dev *scu;
 static DEFINE_MUTEX(scu_lock);
 
 /* IOCTL commands */