modesetting: set driverPrivate to NULL after closing fd.

Otherwise ms_ent_priv will return NULL and things will fall apart.

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

hw/xfree86/drivers/modesetting/driver.c

@@ -635,7 +635,6 @@ FreeRec(ScrnInfoPtr pScrn)
     ms = modesettingPTR(pScrn);
     if (!ms)
         return;
-    pScrn->driverPrivate = NULL;
 
     if (ms->fd > 0) {
         modesettingEntPtr ms_ent;
@@ -656,6 +655,7 @@ FreeRec(ScrnInfoPtr pScrn)
             ms_ent->fd = 0;
         }
     }
+    pScrn->driverPrivate = NULL;
     free(ms->drmmode.Options);
     free(ms);