cifsd: use file_inode() instead of d_inode()

use file_inode() to get layerd filesystems right.
Signed-off-by: Hyunchul Lee <hyc.lee@gmail.com>
Signed-off-by: Namjae Jeon <namjae.jeon@samsung.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifsd/vfs.c

@@ -335,7 +335,7 @@ int ksmbd_vfs_read(struct ksmbd_work *work, struct ksmbd_file *fp, size_t count,
 
 	rbuf = work->aux_payload_buf;
 	filp = fp->filp;
-	inode = d_inode(filp->f_path.dentry);
+	inode = file_inode(filp);
 	if (S_ISDIR(inode->i_mode))
 		return -EISDIR;