dri: Fix problems with unitialized values in dri screen object.

This fixes crash in r200 KMS driver when pSAREA was set to 1 randomly because of memory wasn't cleared.

Signed-off-by: Pauli Nieminen <suokkos@gmail.com>

src/mesa/drivers/dri/common/dri_util.c

@@ -763,7 +763,7 @@ dri2CreateNewScreen(int scrn, int fd,
     if (driDriverAPI.InitScreen2 == NULL)
         return NULL;
 
-    psp = _mesa_malloc(sizeof(*psp));
+    psp = _mesa_calloc(sizeof(*psp));
     if (!psp)
 	return NULL;