[GFS2] Remove unused function from inode.c

The gfs2_glock_nq_m_atime function is unused in so far as its only
ever called with num_gh = 1, and this falls through to the
gfs2_glock_nq_atime function, so we might as well call that directly.

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>