FROMLIST: maple_tree: Adjust node allocation on mas_rebalance()

mas_rebalance() is called to rebalance an insufficient node into a
single node or two sufficient nodes.  The preallocation estimate is
always too many in this case as the height of the tree will never grow
and there is no possibility to have a three way split in this case, so
revise the node allocation count.

Change-Id: I04ba0674da381c06d4f8077f9f59d64b7d1a8312
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Link: https://lore.kernel.org/all/20230612203953.2093911-9-Liam.Howlett@oracle.com/


Bug: 274059236
Signed-off-by: Suren Baghdasaryan <surenb@google.com>