phy: ti: am654-serdes: Constify regmap_config

regmap_config is not modified and can be made static to allow the compiler
to put it in read-only memory.

Before:
   text    data     bss     dec     hex filename
  12328    3644      64   16036    3ea4 drivers/phy/ti/phy-am654-serdes.o

After:
   text    data     bss     dec     hex filename
  12648    3324      64   16036    3ea4 drivers/phy/ti/phy-am654-serdes.o
Signed-off-by: Rikard Falkeborn <rikard.falkeborn@gmail.com>
Link: https://lore.kernel.org/r/20200524095516.25227-2-rikard.falkeborn@gmail.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/phy/ti/phy-am654-serdes.c

@@ -72,7 +72,7 @@ struct serdes_am654_clk_mux {
 #define to_serdes_am654_clk_mux(_hw)	\
 		container_of(_hw, struct serdes_am654_clk_mux, hw)
 
-static struct regmap_config serdes_am654_regmap_config = {
+static const struct regmap_config serdes_am654_regmap_config = {
 	.reg_bits = 32,
 	.val_bits = 32,
 	.reg_stride = 4,