staging: lustre: fix comparison between signed and unsigned

Cleanup in general headers.
* use size_t in cfs_size_round*()
* make unsigned index and len in lustre_cfg_*()
* make iteration variable the same type as comparing value
* make unsigned pages counters

Signed-off-by: Dmitry Eremin <dmitry.eremin@intel.com>
Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-5417
Reviewed-on: http://review.whamcloud.com/11327


Reviewed-by: John L. Hammond <john.hammond@intel.com>
Reviewed-by: Fan Yong <fan.yong@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>
Signed-off-by: James Simmons <jsimmons@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>