maple_tree: use height and depth consistently

maple_tree: use height and depth consistently

For the maple tree, the root node is defined to have a depth of 0 with a
height of 1.  Each level down from the node, these values are incremented
by 1.  Various code paths define a root with depth 1 which is inconsisent
with the definition.  Modify the code to be consistent with this
definition.

Link: https://lkml.kernel.org/r/20250227204823.758784-3-sidhartha.kumar@oracle.com
Signed-off-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>