arm64: perf: Convert snprintf to sysfs_emit

Use sysfs_emit instead of snprintf to avoid buf overrun,because in
sysfs_emit it strictly checks whether buf is null or buf whether
pagesize aligned, otherwise it returns an error.
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1621497585-30887-1-git-send-email-tiantao6@hisilicon.comSigned-off-by: Will Deacon <will@kernel.org>

arch/arm64/kernel/perf_event.c

@@ -312,7 +312,7 @@ static ssize_t slots_show(struct device *dev, struct device_attribute *attr,
 	struct arm_pmu *cpu_pmu = container_of(pmu, struct arm_pmu, pmu);
 	u32 slots = cpu_pmu->reg_pmmir & ARMV8_PMU_SLOTS_MASK;
 
-	return snprintf(page, PAGE_SIZE, "0x%08x\n", slots);
+	return sysfs_emit(page, "0x%08x\n", slots);
 }
 
 static DEVICE_ATTR_RO(slots);