maple_tree: fix testing mas_empty_area()

maple_tree: fix testing mas_empty_area()

Empty area will return -EINVAL if the search window is smaller than the
requested size.  Fix the test case to check for this error code.

Link: https://lkml.kernel.org/r/20230518145544.1722059-27-Liam.Howlett@oracle.com
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Cc: David Binderman <dcb314@hotmail.com>
Cc: Peng Zhang <zhangpeng.00@bytedance.com>
Cc: Sergey Senozhatsky <senozhatsky@chromium.org>
Cc: Vernon Yang <vernon2gm@gmail.com>
Cc: Wei Yang <richard.weiyang@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>