perf/x86/amd/iommu: Make the 'amd_iommu_attr_groups' symbol static

perf/x86/amd/iommu: Make the 'amd_iommu_attr_groups' symbol static

Fixes the following sparse warning:

  arch/x86/events/amd/iommu.c:396:30: warning:
   symbol 'amd_iommu_attr_groups' was not declared. Should it be static?

Signed-off-by: Wang Hai <wanghai26@huawei.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: acme@kernel.org
Cc: alexander.shishkin@linux.intel.com
Cc: bp@alien8.de
Cc: jolsa@redhat.com
Cc: namhyung@kernel.org
Fixes: 51686546304f (x86/events/amd/iommu: Fix sysfs perf attribute groups)
Link: http://lkml.kernel.org/r/20190508020418.19568-1-wanghai26@huawei.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>