Convert printk to current pr_foo() logging functions.

Also add pr_fmt based on KBUILD_MODNAME to avoid repeating prefix.  Prefix
is now "atomic64_test: "
Signed-off-by: NFabian Frederick <fabf@skynet.be>
Cc: Luca Barbieri <luca@luca-barbieri.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>