maple_tree: fix comment typo with corresponding maple_status

maple_tree: fix comment typo with corresponding maple_status

In comment of function mas_start(), we list the return value of different
cases.  According to the comment context, tell the maple_status here is
more consistent with others.

Let's correct it with ma_active in the case it's a tree.

Link: https://lkml.kernel.org/r/20240812150925.31551-2-richard.weiyang@gmail.com
Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
Reviewed-by: Liam R. Howlett <Liam.Howlett@Oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>