phy: cadence: Sierra: Constify a u32[]

'cdns_sierra_pll_mux_table' is not modified in this driver.
And it is only used as a "const u32 *".

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
  60937	   3894	     16	  64847	   fd4f	drivers/phy/cadence/phy-cadence-sierra.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  60897	   3878	     16	  64791	   fd17	drivers/phy/cadence/phy-cadence-sierra.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/43d881d52e3c1632ad197d4c2c18b6c481a13b24.1720723132.git.christophe.jaillet@wanadoo.frSigned-off-by: Vinod Koul <vkoul@kernel.org>

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

@@ -310,7 +310,7 @@ static const struct clk_parent_data pll_mux_parent_data[][SIERRA_NUM_CMN_PLLC_PA
 	},
 };
 
-static u32 cdns_sierra_pll_mux_table[][SIERRA_NUM_CMN_PLLC_PARENTS] = {
+static const u32 cdns_sierra_pll_mux_table[][SIERRA_NUM_CMN_PLLC_PARENTS] = {
 	[CMN_PLLLC] = { 0, 1 },
 	[CMN_PLLLC1] = { 1, 0 },
 };