LU-3319 procfs: update ldiskfs proc handling to seq_files

LU-3319 procfs: update ldiskfs proc handling to seq_files

Migrate all ldiskfs proc handling to using strictly
seq_files. Also include a fix with newer gcc complaining
certain variables are uninitialized.

Signed-off-by: James Simmons <uja.ornl@gmail.com>
Change-Id: Ia296a4682e2feda02bcfbe0100de8a89404cd731
Reviewed-on: http://review.whamcloud.com/8232
Tested-by: Jenkins
Reviewed-by: Nathaniel Clark <nathaniel.l.clark@intel.com>
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Yang Sheng <yang.sheng@intel.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>