net: airoha: Fix register index for Tx-fwd counter configuration

In airoha_qdma_init_qos_stats(), the Tx-fwd counter configuration
register uses the same index (i << 1) as the Tx-cpu counter, which
overwrites the Tx-cpu configuration. The Tx-fwd counter value register
correctly uses (i << 1) + 1, so the configuration register should use
the same index.

Fix the REG_CNTR_CFG index from (i << 1) to ((i << 1) + 1) so that
the Tx-fwd counter is properly configured instead of clobbering the
Tx-cpu counter config.

Fixes: 20bf7d07c956 ("net: airoha: Add sched ETS offload support")
Signed-off-by: Wayen.Yan <win847@gmail.com>
Acked-by: Lorenzo Bianconi <lorenzo@kernel.org>
Link: https://patch.msgid.link/6a2b40e7.4dd82583.3a5c46.e566@mx.google.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>