ocfs2: use 'osb' instead of 'OCFS2_SB()'

We could use 'osb' instead of 'OCFS2_SB()' to make code more elegant.

Link: http://lkml.kernel.org/r/5A702111.7090907@huawei.com
Signed-off-by: Jun Piao <piaojun@huawei.com>
Reviewed-by: Yiwen Jiang <jiangyiwen@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>

fs/ocfs2/aops.c

@@ -2213,7 +2213,7 @@ static int ocfs2_dio_wr_get_block(struct inode *inode, sector_t iblock,
 	down_write(&oi->ip_alloc_sem);
 
 	if (first_get_block) {
-		if (ocfs2_sparse_alloc(OCFS2_SB(inode->i_sb)))
+		if (ocfs2_sparse_alloc(osb))
 			ret = ocfs2_zero_tail(inode, di_bh, pos);
 		else
 			ret = ocfs2_expand_nonsparse_inode(inode, di_bh, pos,