LU-5577 changelog: fix comparison between signed and unsigned

LU-5577 changelog: fix comparison between signed and unsigned

Change type of changelog_*{namelen,size}() to size_t.
Fixed string specifier for unsigned types.

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Change-Id: Ie24c87242328d14ee608ad38b530a6e581db93b9
Reviewed-on: http://review.whamcloud.com/12474
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: James Simmons <uja.ornl@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>
Reviewed-by: James Nunez <james.a.nunez@intel.com>