Fix a bug in fsck_ffs(8) triggered by corrupted filesystems.

The last valid inode in the filesystem is maxino - 1, not maxino.
Thus validity checks should ino < maxino, not ino <= maxino.

Reported-by: Robert Morris
PR: 271312
Sponsored-by: The FreeBSD Foundation

(cherry picked from commit 11ce203e0535c1c8f520c9bda81ab9326cf5db80)