_nfs42_proc_copy(): use ->f_mapping instead of file_inode()->i_mapping

Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/nfs/nfs42proc.c

@@ -336,7 +336,7 @@ static ssize_t _nfs42_proc_copy(struct file *src,
 			return status;
 		}
 	}
-	status = nfs_filemap_write_and_wait_range(file_inode(src)->i_mapping,
+	status = nfs_filemap_write_and_wait_range(src->f_mapping,
 			pos_src, pos_src + (loff_t)count - 1);
 	if (status)
 		return status;