sony-laptop: Avoid oops on module unload for older laptops

Older VAIO laptops without the SN00 ACPI method will have the "handles"
variable unset. Return early from sony_nc_function_cleanup when "handles"
is null.
Signed-off-by: Lawrence Yiu <lawyiu.dev@gmail.com>
Acked-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Darren Hart <dvhart@linux.intel.com>

drivers/platform/x86/sony-laptop.c

@@ -1446,6 +1446,9 @@ static void sony_nc_function_cleanup(struct platform_device *pd)
 {
 	unsigned int i, result, bitmask, handle;
 
+	if (!handles)
+		return;
+
 	/* get enabled events and disable them */
 	sony_nc_int_call(sony_nc_acpi_handle, "SN01", NULL, &bitmask);
 	sony_nc_int_call(sony_nc_acpi_handle, "SN03", &bitmask, &result);