WMI: fix wmi_gtoa() to actully terminate the string

Courtesy of sparse...

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/wmi.c

@@ -220,7 +220,7 @@ static int wmi_gtoa(const char *in, char *out)
 	for (i = 10; i <= 15; i++)
 		out += sprintf(out, "%02X", in[i] & 0xFF);
 
-	out = '\0';
+	*out = '\0';
 	return 0;
 }