perf_events, x86: Fix event constraint masks

Since constraints are specified on the event number, not number
and unit mask shorten the constraint masks so that we'll
actually match something.

Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Stephane Eranian <eranian@google.com>
LKML-Reference: <20100127221121.967610372@chello.nl>
Signed-off-by: Ingo Molnar <mingo@elte.hu>