Removes references to mibstore.h and miInitializeBackingStore, which
have been removed from xorg-server.  Zack Rusin <zackr@vmware.com>
wrote: "It was a noop for at least 5 years and it has been removed."
See: http://patches.openembedded.org/patch/46133/

--- xf86-video-siliconmotion-1.7.7/src/smi_driver.c.~1~	2012-07-17 00:53:21.000000000 -0400
+++ xf86-video-siliconmotion-1.7.7/src/smi_driver.c	2014-12-19 01:30:16.708884086 -0500
@@ -1750,8 +1750,6 @@
 		   "Done writing mode.  Register dump:\n");
     SMI_PrintRegs(pScrn);
 
-    miInitializeBackingStore(pScreen);
-
 #ifdef HAVE_XMODES
     xf86DiDGAInit(pScreen, (unsigned long)(pSmi->FBBase + pScrn->fbOffset));
 #endif
