fix bogus pirq warnings reported in:

  http://bugzilla.kernel.org/show_bug.cgi?id=10366

safe to be backported to v2.6.25 and earlier.

Cc: stable@kernel.org
Signed-off-by: Björn Steinbrink <B.Steinbrink@gmx.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>