gve: Fix RX_BUFFERS_POSTED stat to report per-queue fill_cnt

Previously, the RX_BUFFERS_POSTED stat incorrectly reported the
fill_cnt from RX queue 0 for all queues, resulting in inaccurate
per-queue statistics.
Fix this by correctly indexing priv->rx[idx].fill_cnt for each RX queue.

Fixes: 24aeb56 ("gve: Add Gvnic stats AQ command and ethtool show/set-priv-flags.")
Signed-off-by: Alok Tiwari <alok.a.tiwari@oracle.com>
Link: https://patch.msgid.link/20250527130830.1812903-1-alok.a.tiwari@oracle.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: aloktiwa

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

@@ -2153,7 +2153,7 @@ void gve_handle_report_stats(struct gve_priv *priv)
 			};
 			stats[stats_idx++] = (struct stats) {
 				.stat_name = cpu_to_be32(RX_BUFFERS_POSTED),
-				.value = cpu_to_be64(priv->rx[0].fill_cnt),
+				.value = cpu_to_be64(priv->rx[idx].fill_cnt),
 				.queue_id = cpu_to_be32(idx),
 			};
 		}