perf/powerpc: Fix build error

Fix compile errors like those below:

  CC      arch/powerpc/perf/power7-pmu.o
   /home/git/linux/arch/powerpc/perf/power7-pmu.c:397:2: error: initialization from incompatible pointer type [-Werror]

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Acked-by: Arnaldo Carvalho de Melo <acme@ghostprotocols.net>
Cc: linuxppc-dev@ozlabs.org
Link: http://lkml.kernel.org/r/20130205231938.GA24125@us.ibm.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/powerpc/include/asm/perf_event_server.h

@@ -124,7 +124,7 @@ extern ssize_t power_events_sysfs_show(struct device *dev,
  * POWER CPU specification.
  */
 #define	EVENT_VAR(_id, _suffix)		event_attr_##_id##_suffix
-#define	EVENT_PTR(_id, _suffix)		&EVENT_VAR(_id, _suffix)
+#define	EVENT_PTR(_id, _suffix)		&EVENT_VAR(_id, _suffix).attr.attr
 
 #define	EVENT_ATTR(_name, _id, _suffix)					\
 	PMU_EVENT_ATTR(_name, EVENT_VAR(_id, _suffix), PME_PM_##_id,	\