Apply by doing:
       cd /usr/src
       patch -p0 < 013_brooktree.patch

And then rebuild your kernel.

Index: sys/dev/pci/brooktree848.c
===================================================================
RCS file: /cvs/src/sys/dev/pci/brooktree848.c,v
retrieving revision 1.7
diff -u -r1.7 brooktree848.c
--- sys/dev/pci/brooktree848.c  1999/02/19 02:54:38     1.7
+++ sys/dev/pci/brooktree848.c  1999/11/14 01:59:56
@@ -1,4 +1,4 @@
-/*     $OpenBSD: brooktree848.c,v 1.7 1999/02/19 02:54:38 deraadt Exp $        */
+/* $OpenBSD: brooktree848.c,v 1.12 1999/10/31 20:50:04 deraadt Exp $ */
/* $FreeBSD: brooktree848.c,v 1.64 1999/01/28 17:47:47 roger Exp $ */
/* BT848 Driver for Brooktree's Bt848, Bt849, Bt878 and Bt 879 based cards.
   The Brooktree  BT848 Driver driver is based upon Mark Tinguely and
@@ -1939,14 +1939,15 @@
       int             unit;

       unit = UNIT( minor(dev) );
-       if (unit >= NBKTR)                      /* unit out of range */
+       if (unit >= NBKTR || unit > bktr_cd.cd_ndevs)   /* unit out of range */
               return( ENXIO );

-#if defined(__NetBSD__) || defined(__OpenBSD__)
+       if (bktr_cd.cd_devs == NULL)
+               return( ENXIO );
+
       bktr = bktr_cd.cd_devs[unit];
-#else
-       bktr = &(brooktree[ unit ]);
-#endif
+       if (bktr == NULL)
+               return ( ENXIO );

       if (!(bktr->flags & METEOR_INITALIZED)) /* device not found */
               return( ENXIO );