[GFS2] Eliminate the no longer needed sd_statfs_mutex

This patch eliminates the unneeded sd_statfs_mutex mutex but preserves
the ordering as discussed.

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

diff --cc fs/gfs2/incore.h
Simple merge

diff --cc fs/gfs2/ops_fstype.c
Simple merge

diff --cc fs/gfs2/super.c
Simple merge