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/readdir.c b/fs/cifs/readdir.c
index 586e3d3..d19f199 100644
--- a/fs/cifs/readdir.c
+++ b/fs/cifs/readdir.c
@@ -261,7 +261,7 @@
 	int rc = 0;
 	char *full_path = NULL;
 	struct cifsFileInfo *cifsFile;
-	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 tcon_link *tlink = NULL;
 	struct cifs_tcon *tcon;
 	struct TCP_Server_Info *server;
@@ -561,7 +561,7 @@
 	loff_t first_entry_in_buffer;
 	loff_t index_to_find = pos;
 	struct cifsFileInfo *cfile = 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 = tcon->ses->server;
 	/* check if index in the buffer */
 
@@ -679,7 +679,7 @@
 		char *scratch_buf, unsigned int max_len)
 {
 	struct cifsFileInfo *file_info = file->private_data;
-	struct super_block *sb = file->f_path.dentry->d_sb;
+	struct super_block *sb = file_inode(file)->i_sb;
 	struct cifs_sb_info *cifs_sb = CIFS_SB(sb);
 	struct cifs_dirent de = { NULL, };
 	struct cifs_fattr fattr;