maple_tree: fix mas_find_rev() comment

mas_find_rev() uses mas_prev_entry(), not mas_next_entry(), correct comment.

Link: https://lkml.kernel.org/r/20221025173756.2719616-1-Liam.Howlett@oracle.com


Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>