pipe: kill ->map() and ->unmap()

all pipe_buffer_operations have the same instances of those...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 6928d09..60aafb8 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -901,9 +901,9 @@
 		if (len + offset > PAGE_SIZE)
 			len = PAGE_SIZE - offset;
 
-		src = buf->ops->map(pipe, buf, 1);
+		src = kmap_atomic(buf->page);
 		memcpy(page_address(page) + offset, src + buf->offset, len);
-		buf->ops->unmap(pipe, buf, src);
+		kunmap_atomic(src);
 
 		sg_set_page(&(sgl->sg[sgl->n]), page, len, offset);
 	}