regulator: da9211: Constify struct regulator_desc

'struct regulator_desc' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increase overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  13982	   2118	     16	  16116	   3ef4	drivers/regulator/da9211-regulator.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  14622	   1478	     16	  16116	   3ef4	drivers/regulator/da9211-regulator.o

--
Compile tested only
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/54258bfe11112d70d2f1eb1deda2791eb9ef99c1.1725784852.git.christophe.jaillet@wanadoo.frSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/da9211-regulator.c

@@ -264,7 +264,7 @@ static const struct regulator_ops da9211_buck_ops = {
 	.of_map_mode = da9211_map_buck_mode,\
 }
 
-static struct regulator_desc da9211_regulators[] = {
+static const struct regulator_desc da9211_regulators[] = {
 	DA9211_BUCK(BUCKA),
 	DA9211_BUCK(BUCKB),
 };