powerpc/iommu/debug: fix ifnullfree.cocci warnings

arch/powerpc/kernel/iommu.c:76:2-16: WARNING: NULL check before some freeing functions is not needed.

 NULL check before some freeing functions is not needed.

 Based on checkpatch warning
 "kfree(NULL) is safe this check is probably not required"
 and kfreeaddr.cocci by Julia Lawall.

Generated by: scripts/coccinelle/free/ifnullfree.cocci

Fixes: 691602aa ("powerpc/iommu/debug: Add debugfs entries for IOMMU tables")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: kernel test robot <lkp@intel.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210318234441.GA63469@f8e20a472e81

arch/powerpc/kernel/iommu.c

@@ -72,8 +72,7 @@ static void iommu_debugfs_del(struct iommu_table *tbl)
 
 	sprintf(name, "%08lx", tbl->it_index);
 	liobn_entry = debugfs_lookup(name, iommu_debugfs_dir);
-	if (liobn_entry)
-		debugfs_remove(liobn_entry);
+	debugfs_remove(liobn_entry);
 }
 #else
 static void iommu_debugfs_add(struct iommu_table *tbl){}