sfc: Remove usage of list iterator for list_add() after the loop body

In preparation to limit the scope of a list iterator to the list
traversal loop, use a dedicated pointer pointing to the location
where the element should be inserted [1].

Before, the code implicitly used the head when no element was found
when using &new->list. The new 'pos' variable is set to the list head
by default and overwritten if the list exits early, marking the
insertion point for list_add().

Link: https://lore.kernel.org/all/CAHk-=wgRr_D8CB-D9Kg-c=EHreAsk5SqXPwr9Y7k9sA6cWXJ6w@mail.gmail.com/ [1]
Signed-off-by: Jakob Koschel <jakobkoschel@gmail.com>

drivers/net/ethernet/sfc/rx_common.c

@@ -558,16 +558,18 @@ efx_rx_packet_gro(struct efx_channel *channel, struct efx_rx_buffer *rx_buf,
  */
 struct efx_rss_context *efx_alloc_rss_context_entry(struct efx_nic *efx)
 {
-	struct list_head *head = &efx->rss_context.list;
+	struct list_head *head = *pos = &efx->rss_context.list;
 	struct efx_rss_context *ctx, *new;
 	u32 id = 1; /* Don't use zero, that refers to the master RSS context */
 
 	WARN_ON(!mutex_is_locked(&efx->rss_lock));
 
 	/* Search for first gap in the numbering */
 	list_for_each_entry(ctx, head, list) {
-		if (ctx->user_id != id)
+		if (ctx->user_id != id) {
+			pos = &ctx->list;
 			break;
+		}
 		id++;
 		/* Check for wrap.  If this happens, we have nearly 2^32
 		 * allocated RSS contexts, which seems unlikely.
@@ -585,7 +587,7 @@ struct efx_rss_context *efx_alloc_rss_context_entry(struct efx_nic *efx)
 
 	/* Insert the new entry into the gap */
 	new->user_id = id;
-	list_add_tail(&new->list, &ctx->list);
+	list_add_tail(&new->list, pos);
 	return new;
 }