excessive checks in ufs_write_failed() and ufs_evict_inode()

As it is, short copy in write() to append-only file will fail
to truncate the excessive allocated blocks.  As the matter of
fact, all checks in ufs_truncate_blocks() are either redundant
or wrong for that caller.  As for the only other caller
(ufs_evict_inode()), we only need the file type checks there.

Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>