f2fs: fix incomplete block usage in compact SSA summaries

f2fs: fix incomplete block usage in compact SSA summaries

In a previous commit, a bug was introduced where compact SSA summaries
failed to utilize the entire block space in non-4KB block size
configurations, leading to inefficient space management.

This patch fixes the calculation logic to ensure that compact SSA
summaries can fully occupy the block regardless of the block size.

Reported-by: Chris Mason <clm@meta.com>
Fixes: e48e16f3e37f ("f2fs: support non-4KB block size without packed_ssa feature")
Signed-off-by: Daeho Jeong <daehojeong@google.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>