dix: fix a -Wshadow warning

dispatch.c: In function 'SetVendorString':
dispatch.c:481:29: warning: declaration of 'string' shadows a global declaration [-Wshadow]
 SetVendorString(const char *string)
                             ^
dispatch.c:135:21: warning: shadowed declaration is here [-Wshadow]
 typedef const char *string;

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Keith Packard <keithp@keithp.com>

dix/dispatch.c

@@ -478,9 +478,9 @@ SetVendorRelease(int release)
 }
 
 void
-SetVendorString(const char *string)
+SetVendorString(const char *vendor)
 {
-    VendorString = string;
+    VendorString = vendor;
 }
 
 Bool