[GFS2] Tidy up dir code as per Christoph Hellwig's comments

1. Comment whitespace fix
2. Removed unused header files from dir.c
3. Split the gfs2_dir_get_buffer() function into two functions

Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/dir.h

@@ -41,8 +41,8 @@ int gfs2_dir_exhash_dealloc(struct gfs2_inode *dip);
 
 int gfs2_diradd_alloc_required(struct inode *dir,
 			       const struct qstr *filename);
-int gfs2_dir_get_buffer(struct gfs2_inode *ip, uint64_t block, int new,
-                        struct buffer_head **bhp);
+int gfs2_dir_get_new_buffer(struct gfs2_inode *ip, uint64_t block,
+			    struct buffer_head **bhp);
 
 static inline uint32_t gfs2_disk_hash(const char *data, int len)
 {