mm: drop useless local parameters of __register_one_node()

mm: drop useless local parameters of __register_one_node()

__register_one_node() initializes local parameters "p_node" & "parent"
for register_node().

But, register_node() does not use them.

Remove the related code of "parent" node, cleanup __register_one_node()
and register_node().

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Dou Liyang <[email protected]>
Acked-by: David Rientjes <[email protected]>
Acked-by: Michal Hocko <[email protected]>
Cc: <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>