net: pcs: xpcs: mask readl() return value to 16 bits

readl() returns 32-bit value but Clause 22/45 registers are 16-bit wide.
Masking with 0xFFFF avoids using garbage upper bits.

Signed-off-by: Jack Ping CHNG <jchng@maxlinear.com>
Reviewed-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: NipaLocal <nipa@local>

Author: Jack Ping CHNG

drivers/net/pcs/pcs-xpcs-plat.c

@@ -66,7 +66,7 @@ static int xpcs_mmio_read_reg_indirect(struct dw_xpcs_plat *pxpcs,
 	switch (pxpcs->reg_width) {
 	case 4:
 		writel(page, pxpcs->reg_base + (DW_VR_CSR_VIEWPORT << 2));
-		ret = readl(pxpcs->reg_base + (ofs << 2));
+		ret = readl(pxpcs->reg_base + (ofs << 2)) & 0xffff;
 		break;
 	default:
 		writew(page, pxpcs->reg_base + (DW_VR_CSR_VIEWPORT << 1));
@@ -124,7 +124,7 @@ static int xpcs_mmio_read_reg_direct(struct dw_xpcs_plat *pxpcs,
 
 	switch (pxpcs->reg_width) {
 	case 4:
-		ret = readl(pxpcs->reg_base + (csr << 2));
+		ret = readl(pxpcs->reg_base + (csr << 2)) & 0xffff;
 		break;
 	default:
 		ret = readw(pxpcs->reg_base + (csr << 1));