ceph: use ceph_sb_to_client instead of ceph_client

ceph_sb_to_client and ceph_client are really identical, we need to dump
one; while function ceph_client is confusing with "struct ceph_client",
ceph_sb_to_client's definition is more clear; so we'd better switch all
call to ceph_sb_to_client.

  -static inline struct ceph_client *ceph_client(struct super_block *sb)
  -{
  -	return sb->s_fs_info;
  -}

Signed-off-by: Cheng Renquan <crquan@gmail.com>
Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/file.c b/fs/ceph/file.c
index 6230c3d..834d2b8 100644
--- a/fs/ceph/file.c
+++ b/fs/ceph/file.c
@@ -809,7 +809,7 @@
 	struct file *file = iocb->ki_filp;
 	struct inode *inode = file->f_dentry->d_inode;
 	struct ceph_inode_info *ci = ceph_inode(inode);
-	struct ceph_osd_client *osdc = &ceph_client(inode->i_sb)->osdc;
+	struct ceph_osd_client *osdc = &ceph_sb_to_client(inode->i_sb)->osdc;
 	loff_t endoff = pos + iov->iov_len;
 	int got = 0;
 	int ret, err;