net: mtk_eth_soc: delete an unneeded variable

There is already an "int err" declared at the start of the function so
re-use that instead of declaring a shadow err variable.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20211217070735.GC26548@kiliSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.c

@@ -2211,7 +2211,6 @@ static int mtk_open(struct net_device *dev)
 	/* we run 2 netdevs on the same dma ring so we only bring it up once */
 	if (!refcount_read(&eth->dma_refcnt)) {
 		u32 gdm_config = MTK_GDMA_TO_PDMA;
-		int err;
 
 		err = mtk_start_dma(eth);
 		if (err)