perf/x86/amd: Fix RDPMC index calculation for AMD family 15h

perf/x86/amd: Fix RDPMC index calculation for AMD family 15h

The RDPMC index calculation is wrong for AMD family 15h
(X86_FEATURE_ PERFCTR_CORE set). This leads to a #GP when
accessing the counter:

 Pid: 2237, comm: syslog-ng Not tainted 3.5.0-rc1-perf-x86_64-standard-g130ff90 #135 AMD Pike/Pike
 RIP: 0010:[<ffffffff8100dc33>]  [<ffffffff8100dc33>] x86_perf_event_update+0x27/0x66

While the msr address offset is (index << 1) we must use index to
select the correct rdpmc.

Signed-off-by: Robert Richter <[email protected]>
Acked-by: Peter Zijlstra <[email protected]>
Cc: Vince Weaver <[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>