x86: mmiotrace: quieten spurious warning message

This message was being incorrectly emitted when using gdb,
so compile it out by default for now; there will be a
better fix in v2.6.30.

Reported-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Stuart Bennett <stuart@freedesktop.org>
Acked-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>