perf/arm-cmn: Make arm_cmn_debugfs static

Indeed our debugfs directory is driver-internal so should be static.

Link: https://lore.kernel.org/r/202202030812.II1K2ZXf-lkp@intel.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Link: https://lore.kernel.org/r/ca9248caaae69b5134f69e085fe78905dfe74378.1643911278.git.robin.murphy@arm.comSigned-off-by: Will Deacon <will@kernel.org>

drivers/perf/arm-cmn.c

@@ -353,7 +353,7 @@ static struct arm_cmn_node *arm_cmn_node(const struct arm_cmn *cmn,
 	return NULL;
 }
 
-struct dentry *arm_cmn_debugfs;
+static struct dentry *arm_cmn_debugfs;
 
 #ifdef CONFIG_DEBUG_FS
 static const char *arm_cmn_device_type(u8 type)