net: ethernet: mtk_wed: fix EXT_INT_STATUS_RX_FBUF definitions for MT7986 SoC

Fix MTK_WED_EXT_INT_STATUS_RX_FBUF_LO_TH and
MTK_WED_EXT_INT_STATUS_RX_FBUF_HI_TH definitions for MT7986 (MT7986 is
the only SoC to use them).

Fixes: de84a090 ("net: ethernet: mtk_eth_wed: add wed support for mt7986 chipset")
Signed-off-by: Lorenzo Bianconi <lorenzo@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>