kernel: kmod-stmmac-core: fix CONFIG_DWMAC_DWC_QOS_ETH typo

The symbol was listed as CONFIG_CONFIG_DWMAC_DWC_QOS_ETH, so the
intended override never took effect. Fix the doubled prefix.

No functional change: kmod-stmmac-core is only available on armsr,
loongarch64 and x86_64, where CONFIG_DWMAC_DWC_QOS_ETH is already
disabled in the generic kernel config.

Fixes: 1816e53062 ("armsr: Move kmod-stmmac-core to common place")
Signed-off-by: Sander van Deijck <sander@vandeijck.com>
Link: https://github.com/openwrt/openwrt/pull/25965
Signed-off-by: Robert Marko <robimarko@gmail.com>

package/kernel/linux/modules/netdevices.mk

@@ -2213,7 +2213,7 @@ define KernelPackage/stmmac-core
   KCONFIG:=CONFIG_STMMAC_ETH \
     CONFIG_STMMAC_SELFTESTS=n \
     CONFIG_STMMAC_PLATFORM \
-    CONFIG_CONFIG_DWMAC_DWC_QOS_ETH=n \
+    CONFIG_DWMAC_DWC_QOS_ETH=n \
     CONFIG_DWMAC_GENERIC
   FILES=$(LINUX_DIR)/drivers/net/ethernet/stmicro/stmmac/stmmac.ko \
     $(LINUX_DIR)/drivers/net/ethernet/stmicro/stmmac/stmmac-platform.ko \