pipe: fold file_operations instances in one

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

fs/internal.h

@@ -130,3 +130,8 @@ extern struct dentry *__d_alloc(struct super_block *, const struct qstr *);
  * read_write.c
  */
 extern ssize_t __kernel_write(struct file *, const char *, size_t, loff_t *);
+
+/*
+ * pipe.c
+ */
+extern const struct file_operations pipefifo_fops;