[GFS2] Directory code style changes

As per comments from Jan Engelhardt, remove redundant casts, redundant
endian conversions, add a smattering of const and rewrite the
dirent_next function in order to avoid as many casts as possible.

Cc: Jan Engelhardt <jengelh@linux01.gwdg.de>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>
diff --git a/fs/gfs2/ops_super.c b/fs/gfs2/ops_super.c
index 820db93..addcf13 100644
--- a/fs/gfs2/ops_super.c
+++ b/fs/gfs2/ops_super.c
@@ -190,8 +190,7 @@
 
 static void gfs2_unlockfs(struct super_block *sb)
 {
-	struct gfs2_sbd *sdp = sb->s_fs_info;
-	gfs2_unfreeze_fs(sdp);
+	gfs2_unfreeze_fs(sb->s_fs_info);
 }
 
 /**