i386: Fix wrong CPU error message in early boot path

- boot/setup.S did not print "PANIC: CPU too old for this kernel"
  ( not visible, also the message did not match )
- I add "# missed before: set ds"
  => somebody should check if I am right with the way to set.
  => seems to be a generic error in setup.S not to set "ds" for error messages.

AK: extracted patch out of other changes
AK: also couldn't find any other case where ds is wrong
Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>