[PATCH v3 6/7] Mute some compiler warnings.

This patch mutes follwing compiler warnings:
  - warning: assignment discards ‘const’ qualifier from
    pointer target type [enabled by default],
  - warning: variable ‘page_offset’ set but not used
    [-Wunused-but-set-variable].

v2 - suggestions/fixes:
   - do not discard a const qualifier
     (suggested by Andrew Cooper).

Signed-off-by: Daniel Kiper <daniel.kiper@oracle.com>