dix: tables.c should include header that defines InitialVector

Clears warning from clang 19.1.7:

dix/tables.c:59:7: warning: no previous extern declaration for non-static
 variable 'InitialVector' [-Wmissing-variable-declarations]
   59 | int (*InitialVector[3]) (ClientPtr /* client */) = {
      |       ^

Fixes: bae6cbc8c ("include: move private defs to dixstruct_priv.h")
Signed-off-by: Alan Coopersmith <alan.coopersmith@oracle.com>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1910>

dix/tables.c

@@ -51,6 +51,7 @@ SOFTWARE.
 #include "windowstr.h"
 #include "extnsionst.h"
 #include "dixstruct.h"
+#include "dixstruct_priv.h"
 #include "dixevents.h"
 #include "dispatch.h"
 #include "swaprep.h"