maple_tree: change mas_adopt_children() parent usage

All calls to mas_adopt_children() currently pass the parent as the node in
the maple state.  Allow for the parent pointer that is passed in to be
used instead.

Link: https://lkml.kernel.org/r/20230804165951.2661157-6-Liam.Howlett@oracle.com


Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Paul E. McKenney <paulmck@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>