x86/events/amd/iommu: Fix sysfs type mismatch

dev_attr_show() calls _iommu_event_show() via an indirect call but
_iommu_event_show()'s type does not currently match the type of the
show() member in 'struct device_attribute', resulting in a Control Flow
Integrity violation.

$ cat /sys/devices/amd_iommu_1/events/mem_dte_hit
csource=0x0a

$ dmesg | grep "CFI failure"
[ 3526.735140] CFI failure (target: _iommu_event_show...):

Change _iommu_event_show() and 'struct amd_iommu_event_desc' to
'struct device_attribute' so that there is no more CFI violation.

Fixes: 7be6296f ("perf/x86/amd: AMD IOMMU Performance Counter PERF uncore PMU implementation")
Signed-off-by: Nathan Chancellor <nathan@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20210415001112.3024673-1-nathan@kernel.org

arch/x86/events/amd/iommu.c

@@ -81,12 +81,12 @@ static struct attribute_group amd_iommu_events_group = {
 };
 
 struct amd_iommu_event_desc {
-	struct kobj_attribute attr;
+	struct device_attribute attr;
 	const char *event;
 };
 
-static ssize_t _iommu_event_show(struct kobject *kobj,
-				struct kobj_attribute *attr, char *buf)
+static ssize_t _iommu_event_show(struct device *dev,
+				struct device_attribute *attr, char *buf)
 {
 	struct amd_iommu_event_desc *event =
 		container_of(attr, struct amd_iommu_event_desc, attr);