perf/x86/intel/uncore: Fix for iio mapping on Skylake Server

Introduced early attributes /sys/devices/uncore_iio_<pmu_idx>/die* are
initialized by skx_iio_set_mapping(), however, for example, for multiple
segment platforms skx_iio_get_topology() returns -EPERM before a list of
attributes in skx_iio_mapping_group will have been initialized.
As a result the list is being NULL. Thus the warning
"sysfs: (bin_)attrs not set by subsystem for group: uncore_iio_*/" appears
and uncore_iio pmus are not available in sysfs. Clear IIO attr_update
to properly handle the cases when topology information cannot be
retrieved.

Fixes: bb42b3d3 ("perf/x86/intel/uncore: Expose an Uncore unit to IIO PMON mapping")
Reported-by: Kyle Meyer <kyle.meyer@hpe.com>
Suggested-by: Kan Liang <kan.liang@linux.intel.com>
Signed-off-by: Alexander Antonov <alexander.antonov@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Alexei Budankov <alexey.budankov@linux.intel.com>
Reviewed-by: Kan Liang <kan.liang@linux.intel.com>
Link: https://lkml.kernel.org/r/20200928102133.61041-1-alexander.antonov@linux.intel.com

arch/x86/events/intel/uncore_snbep.c

@@ -3754,7 +3754,9 @@ static int skx_iio_set_mapping(struct intel_uncore_type *type)
 
 	ret = skx_iio_get_topology(type);
 	if (ret)
-		return ret;
+		goto clear_attr_update;
+
+	ret = -ENOMEM;
 
 	/* One more for NULL. */
 	attrs = kcalloc((uncore_max_dies() + 1), sizeof(*attrs), GFP_KERNEL);
@@ -3786,8 +3788,9 @@ static int skx_iio_set_mapping(struct intel_uncore_type *type)
 	kfree(eas);
 	kfree(attrs);
 	kfree(type->topology);
+clear_attr_update:
 	type->attr_update = NULL;
-	return -ENOMEM;
+	return ret;
 }
 
 static void skx_iio_cleanup_mapping(struct intel_uncore_type *type)