ufs: restore uniqueness of st_dev

[chs]

Summary

the recently-added ufs_stat() sets st_dev to vp->v_mount->mnt_stat.f_fsid.val[0], but that value is not guaranteed to be unique, only the full 64-bit mnt_stat.f_fsid is guaranteed to be unique. ufs in particular stores the fsid in the superblock at newfs time, and the first 32-bit half is set to the time_t of when newfs was run, so if two file systems are newfs'd in the same second (easy to do with flash storage) then ufs_stat() will report the same st_dev for both file systems. this patch restores uniqueness of st_dev for ufs file systems by changing ufs_stat() to set st_dev to the same value that we used to get before the VOP_STAT() changes.

[mjg]

doh

[imp]

All the other filesystems set this to the dev. UFS sets it to a time...