jffs2: Convert printks to pr_<level>

Use the more current logging style.

Coalesce formats, align arguments.
Convert uses of embedded function names to %s, __func__.

A couple of long line checkpatch errors I don't care about exist.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@linux.intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>