phy: cadence: Sierra: Constify struct cdns_reg_pairs

'struct cdns_reg_pairs' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  60489	   4342	     16	  64847	   fd4f	drivers/phy/cadence/phy-cadence-sierra.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  60521	   4310	     16	  64847	   fd4f	drivers/phy/cadence/phy-cadence-sierra.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/c57ee8206ebba8c222d7d954335654384072b9ac.1720723132.git.christophe.jaillet@wanadoo.frSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/cadence/phy-cadence-sierra.c

@@ -1544,7 +1544,7 @@ static void cdns_sierra_phy_remove(struct platform_device *pdev)
 }
 
 /* SGMII PHY PMA lane configuration */
-static struct cdns_reg_pairs sgmii_phy_pma_ln_regs[] = {
+static const struct cdns_reg_pairs sgmii_phy_pma_ln_regs[] = {
 	{0x9010, SIERRA_PHY_PMA_XCVR_CTRL}
 };
 
@@ -1609,7 +1609,7 @@ static struct cdns_sierra_vals sgmii_100_no_ssc_plllc1_opt3_ln_vals = {
 };
 
 /* QSGMII PHY PMA lane configuration */
-static struct cdns_reg_pairs qsgmii_phy_pma_ln_regs[] = {
+static const struct cdns_reg_pairs qsgmii_phy_pma_ln_regs[] = {
 	{0x9010, SIERRA_PHY_PMA_XCVR_CTRL}
 };
 
@@ -1675,7 +1675,7 @@ static struct cdns_sierra_vals qsgmii_100_no_ssc_plllc1_ln_vals = {
 };
 
 /* PCIE PHY PCS common configuration */
-static struct cdns_reg_pairs pcie_phy_pcs_cmn_regs[] = {
+static const struct cdns_reg_pairs pcie_phy_pcs_cmn_regs[] = {
 	{0x0430, SIERRA_PHY_PIPE_CMN_CTRL1}
 };