lib/maple_tree.c: fix build error due to hotfix alteration

Commit 0de56e38 ("maple_tree: use maple state end for write
operations") was broken by a later patch "maple_tree: do not preallocate
nodes for slot stores".  But the later patch was scheduled ahead of
0de56e38, for 6.7-rc.

This fixlet undoes the damage.

Fixes: 0de56e38 ("maple_tree: use maple state end for write operations")
Cc: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>