This patch makes the kernel VESA driver silently ignore failure to
enable write-combining for the frame-buffer region using MTRR's.

I have a Toshiba Libretto 50CT which has an original Pentium processor
(P54C) which doesn't have MTRR's.  Since write combining is a performance
optimization, not a correctness issue, I'd rather have a slow /dev/draw
(which I'm already used to on that machine) instead of none at all.