get rid of pipe->inode

it's used only as a flag to distinguish normal pipes/FIFOs from the
internal per-task one used by file-to-file splice.  And pipe->files
would work just as well for that purpose...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/pipe.c

@@ -55,7 +55,7 @@ unsigned int pipe_min_size = PAGE_SIZE;
 
 static void pipe_lock_nested(struct pipe_inode_info *pipe, int subclass)
 {
-	if (pipe->inode)
+	if (pipe->files)
 		mutex_lock_nested(&pipe->mutex, subclass);
 }
 
@@ -70,7 +70,7 @@ EXPORT_SYMBOL(pipe_lock);
 
 void pipe_unlock(struct pipe_inode_info *pipe)
 {
-	if (pipe->inode)
+	if (pipe->files)
 		mutex_unlock(&pipe->mutex);
 }
 EXPORT_SYMBOL(pipe_unlock);
@@ -785,7 +785,6 @@ struct pipe_inode_info * alloc_pipe_info(struct inode *inode)
 		if (pipe->bufs) {
 			init_waitqueue_head(&pipe->wait);
 			pipe->r_counter = pipe->w_counter = 1;
-			pipe->inode = inode;
 			pipe->buffers = PIPE_DEF_BUFFERS;
 			mutex_init(&pipe->mutex);
 			return pipe;