powerpc/pseries: add of_node_put() in dlpar_detach_node()

The previous commit, "of: overlay: add missing of_node_get() in
__of_attach_node_sysfs" added a missing of_node_get() to
__of_attach_node_sysfs().  This results in a refcount imbalance
for nodes attached with dlpar_attach_node().  The calling sequence
from dlpar_attach_node() to __of_attach_node_sysfs() is:

   dlpar_attach_node()
      of_attach_node()
         __of_attach_node_sysfs()

For more detailed description of the node refcount, see
commit 68baf692 ("powerpc/pseries: Fix of_node_put() underflow
during DLPAR remove").
Tested-by: Alan Tull <atull@kernel.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Frank Rowand <frank.rowand@sony.com>

arch/powerpc/platforms/pseries/dlpar.c

@@ -270,6 +270,8 @@ int dlpar_detach_node(struct device_node *dn)
 	if (rc)
 		return rc;
 
+	of_node_put(dn);
+
 	return 0;
 }