Revert "dm space maps: don't reset space map allocation cursor when committing"

hulk inclusion
category: bugfix
bugzilla: 185894, https://gitee.com/openeuler/kernel/issues/I4SJ8H?from=project-issue


CVE: NA

-----------------------------------------------

This reverts commit b0d9aeb4.

This commit b0d9aeb4 ("dm space maps: don't reset space map allocation
cursor when committing") change the way to find free block.

But when use ramdisk(not support discard) for thin-pool,and storage
over-commitment. Then constantly create and delete file, can find block
in thin-pool, but can't find block in ramdisk.

So need revert this patch.

Signed-off-by: Luo Meng <luomeng12@huawei.com>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>