realtek: pcs: rtl838x: replace literal with macro

Replace 0 with MII_BMCR because in this context, it maps cleanly to
normal PHY register structure. BMCR_PDOWN is already used there to show
which bits are set.

Link: openwrt/openwrt#23746
Signed-off-by: Jonas Jelonek <jelonek.jonas@gmail.com>

Author: jonasjelonek

target/linux/realtek/files-6.18/drivers/net/pcs/pcs-rtl-otto.c

@@ -762,7 +762,7 @@ static int rtpcs_838x_sds_activate(struct rtpcs_serdes *sds)
 	int ret;
 
 	/* CFG_FIB_PDOWN / BMCR_PDOWN */
-	ret = rtpcs_sds_write_bits(sds, 2, 0, 11, 11, 0x0);
+	ret = rtpcs_sds_write_bits(sds, 2, MII_BMCR, 11, 11, 0x0);
 	if (ret)
 		return ret;