selftests: mm: fix the incorrect usage() info of khugepaged

selftests: mm: fix the incorrect usage() info of khugepaged

The mount option of tmpfs should be huge=advise, not madvise which is not
supported and may mislead the users.

Link: https://lkml.kernel.org/r/20241015020257.139235-1-sunnanyong@huawei.com
Fixes: 1b03d0d558a2 ("selftests/vm: add thp collapse file and tmpfs testing")
Signed-off-by: Nanyong Sun <sunnanyong@huawei.com>
Reviewed-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Zach O'Keefe <zokeefe@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>