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);
 
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<div class='path'>path: <a href='/guix/log/?id=213b05f04e2ee246ffb0285c71ad2f646795d135'>root</a>/<a href='/guix/log/gnu?id=213b05f04e2ee246ffb0285c71ad2f646795d135'>gnu</a>/<a href='/guix/log/gnu/bootloader.scm?id=213b05f04e2ee246ffb0285c71ad2f646795d135'>bootloader.scm</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/gnu/bootloader.scm?id=213b05f04e2ee246ffb0285c71ad2f646795d135&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2019-03-24 23:06:11 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=8d058e7b1b1a409d3d9cc29c5650a98db4e78783'>bootloader: Add a 'keyboard-layout' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-24 23:06:10 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=91b6873b24c205bd445844845fb44add643d0cff'>bootloader: Reindent record type definition.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-03-24 23:06:10 +0100'>2019-03-24</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=8a0e1bb12b3c22a8c9a2be17492058ca63ec7c5d'>bootloader: Remove unused 'additional-configuration' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2019-01-16 14:07:38 +0100'>2019-01-16</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=5f7467f046c3c1648cdf6eb81b3ec041bfc1f9bb'>bootloader: Remove deprecated 'device' field.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2018-04-08 17:48:33 +0200'>2018-04-08</span></td><td><a href='/guix/commit/gnu/bootloader.scm?id=3c0128b035ae00462f1b0a4427d9525d750e5575'>discovery: Remove dependency on (guix ui).</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>