cifs: get rid of ->f_path.dentry->d_sb uses, add a new helper

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/cifs/file.c b/fs/cifs/file.c
index 3e4d00a..d535e16 100644
--- a/fs/cifs/file.c
+++ b/fs/cifs/file.c
@@ -1586,7 +1586,7 @@
 	cifs_read_flock(flock, &type, &lock, &unlock, &wait_flag,
 			tcon->ses->server);
 
-	cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	cifs_sb = CIFS_FILE_SB(file);
 	netfid = cfile->fid.netfid;
 	cinode = CIFS_I(file_inode(file));
 
@@ -2305,7 +2305,7 @@
 	struct cifs_tcon *tcon;
 	struct TCP_Server_Info *server;
 	struct cifsFileInfo *smbfile = file->private_data;
-	struct cifs_sb_info *cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	struct cifs_sb_info *cifs_sb = CIFS_FILE_SB(file);
 	struct inode *inode = file->f_mapping->host;
 
 	rc = filemap_write_and_wait_range(inode->i_mapping, start, end);
@@ -2585,7 +2585,7 @@
 	iov_iter_truncate(from, len);
 
 	INIT_LIST_HEAD(&wdata_list);
-	cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	cifs_sb = CIFS_FILE_SB(file);
 	open_file = file->private_data;
 	tcon = tlink_tcon(open_file->tlink);
 
@@ -3010,7 +3010,7 @@
 		return 0;
 
 	INIT_LIST_HEAD(&rdata_list);
-	cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	cifs_sb = CIFS_FILE_SB(file);
 	open_file = file->private_data;
 	tcon = tlink_tcon(open_file->tlink);
 
@@ -3155,7 +3155,7 @@
 	__u32 pid;
 
 	xid = get_xid();
-	cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	cifs_sb = CIFS_FILE_SB(file);
 
 	/* FIXME: set up handlers for larger reads and/or convert to async */
 	rsize = min_t(unsigned int, cifs_sb->rsize, CIFSMaxBufSize);
@@ -3462,7 +3462,7 @@
 	int rc;
 	struct list_head tmplist;
 	struct cifsFileInfo *open_file = file->private_data;
-	struct cifs_sb_info *cifs_sb = CIFS_SB(file->f_path.dentry->d_sb);
+	struct cifs_sb_info *cifs_sb = CIFS_FILE_SB(file);
 	struct TCP_Server_Info *server;
 	pid_t pid;