Xi: change XIChangeDeviceProperty from const pointer to const void *

According to Daniel Kurtz, a typedef void *pointer is a atomic type. So a
'const pointer' is equivalent to 'void* const' instead of the intended
'const void*'.

This technically changes the ABI, but we don't bump it for this.

Signed-off-by: Peter Hutterer <peter.hutterer@who-t.net>
Reviewed-by: Chase Douglas <chase.douglas@canonical.com>

include/exevents.h

@@ -92,7 +92,7 @@ extern _X_EXPORT int XIChangeDeviceProperty(
         int                     /* format*/,
         int                     /* mode*/,
         unsigned long           /* len*/,
-        const pointer           /* value*/,
+        const void*             /* value*/,
         Bool                    /* sendevent*/
         );