perf/x86/amd: Do not print an error when the device is not present

perf/x86/amd: Do not print an error when the device is not present

As Linus said its not an error to not have an AMD IOMMU; esp.
when you're not even running on an AMD platform.

Reported-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Acked-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>
Link: http://lkml.kernel.org/r/20130703075542.GF23916@twins.programming.kicks-ass.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>