dm pcache: fix segment info indexing

dm pcache: fix segment info indexing

commit 13ea55ea20176736516b20b9ea2d8cf97dbe74f5 upstream.

Segment info indexing also used sizeof(struct) instead of the
4K metadata stride, so info_index could point between slots and
subsequent writes would advance incorrectly. Derive info_index
from the pointer returned by the segment meta search using
PCACHE_SEG_INFO_SIZE and advance to the next slot for future
updates.

Signed-off-by: Li Chen <chenl311@chinatelecom.cn>
Signed-off-by: Dongsheng Yang <dongsheng.yang@linux.dev>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Zheng Gu <cengku@gmail.com>
Cc: stable@vger.kernel.org	# 6.18
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>