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 <[e-mail]>
Link: https://patch.msgid.link/54258bfe11[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/regulator/da9211-regulator.c

···
 	.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),
 };