ocfs2: remove set but not used variable 'rb'

Fixes gcc '-Wunused-but-set-variable' warning:

fs/ocfs2/refcounttree.c: In function 'ocfs2_create_reflink_node':
fs/ocfs2/refcounttree.c:4138:31: warning:
 variable 'rb' set but not used [-Wunused-but-set-variable]

Link: http://lkml.kernel.org/r/1536198443-113047-1-git-send-email-yuehaibing@huawei.comSigned-off-by: YueHaibing <yuehaibing@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/refcounttree.c

@@ -4135,7 +4135,6 @@ static int ocfs2_create_reflink_node(struct inode *s_inode,
 	struct buffer_head *ref_root_bh = NULL;
 	struct ocfs2_cached_dealloc_ctxt dealloc;
 	struct ocfs2_super *osb = OCFS2_SB(s_inode->i_sb);
-	struct ocfs2_refcount_block *rb;
 	struct ocfs2_dinode *di = (struct ocfs2_dinode *)s_bh->b_data;
 	struct ocfs2_refcount_tree *ref_tree;
 
@@ -4162,7 +4161,6 @@ static int ocfs2_create_reflink_node(struct inode *s_inode,
 		mlog_errno(ret);
 		goto out;
 	}
-	rb = (struct ocfs2_refcount_block *)ref_root_bh->b_data;
 
 	ret = ocfs2_duplicate_extent_list(s_inode, t_inode, t_bh,
 					  &ref_tree->rf_ci, ref_root_bh,