Remove use of interface no longer provided by xorg-server.

Patch taken from upstream:
https://cgit.freedesktop.org/xorg/driver/xf86-video-sis/commit/?id=4b1356a2b7fd06e9a05d134caa4033681c939737

diff --git a/src/sis_driver.c b/src/sis_driver.c
index 8f06164..513f68b 100644
--- a/src/sis_driver.c
+++ b/src/sis_driver.c
@@ -2738,7 +2738,7 @@ SiSPrintModes(ScrnInfoPtr pScrn)
     float hsync, refresh = 0.0;
     char *desc, *desc2, *prefix, *uprefix, *output;
 
-    xf86DrvMsg(pScrn->scrnIndex, pScrn->virtualFrom, "Virtual size is %dx%d "
+    xf86DrvMsg(pScrn->scrnIndex, X_INFO, "Virtual size is %dx%d "
 	       "(pitch %d)\n", pScrn->virtualX, pScrn->virtualY,
 	       pScrn->displayWidth);