minix: fix error handling in minix_set_link

If minix_prepare_chunk fails, updating c/mtime and marking the
dir inode dirty is wrong, as the inode hasn't been modified.  Also
propagate the error to the caller.

Note that this moves the dir_put_page call later, but that matches
other uses of this helper in the directory code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>