ocfs2: eliminate a misreported warning

ocfs2: eliminate a misreported warning

The warning is invalid because the parameter chunksize passed from
ocfs2_info_freefrag_scan_chain-->ocfs2_info_update_ffg is guaranteed to
be positive.  So __ilog2_u32 cannot return -1.

  fs/ocfs2/ioctl.c: In function 'ocfs2_info_update_ffg':
  fs/ocfs2/ioctl.c:411:17: warning: array subscript is below array bounds [-Warray-bounds]
    hist->fc_chunks[index]++;
                   ^
  fs/ocfs2/ioctl.c:411:17: warning: array subscript is below array bounds [-Warray-bounds]

Link: http://lkml.kernel.org/r/1524655799-12112-1-git-send-email-thunder.leizhen@huawei.com
Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Mark Fasheh <mark@fasheh.com>
Cc: Joel Becker <jlbec@evilplan.org>
Cc: Junxiao Bi <junxiao.bi@oracle.com>
Cc: Joseph Qi <jiangqi903@gmail.com>
Cc: Changwei Ge <ge.changwei@h3c.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>