selftests/mm: fix spelling mistake "mrmeap" -> "mremap"

There are spelling mistakes in perror messages.  Fix these.

Link: https://lkml.kernel.org/r/20250813081333.1978096-1-colin.i.king@gmail.com


Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>