gve: Fix the queue page list allocated pages count

In gve_alloc_queue_page_list(), when a page allocation fails,
qpl->num_entries will be wrong.  In this case priv->num_registered_pages
can underflow in gve_free_queue_page_list(), causing subsequent calls
to gve_alloc_queue_page_list() to fail.

Fixes: f5cedc8 ("gve: Add transmit and receive support")
Signed-off-by: Jeroen de Borst <jeroendb@google.com>
Reviewed-by: Catherine Sullivan <csully@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/google/gve/gve_main.c

@@ -544,7 +544,7 @@ static int gve_alloc_queue_page_list(struct gve_priv *priv, u32 id,
 	}
 
 	qpl->id = id;
-	qpl->num_entries = pages;
+	qpl->num_entries = 0;
 	qpl->pages = kvzalloc(pages * sizeof(*qpl->pages), GFP_KERNEL);
 	/* caller handles clean up */
 	if (!qpl->pages)
@@ -562,6 +562,7 @@ static int gve_alloc_queue_page_list(struct gve_priv *priv, u32 id,
 		/* caller handles clean up */
 		if (err)
 			return -ENOMEM;
+		qpl->num_entries++;
 	}
 	priv->num_registered_pages += pages;