fix(st-pmic): add static const to pmic_ops

The static was found by sparse tool:
drivers/st/pmic/stm32mp_pmic.c:456:18: warning: symbol 'pmic_ops'
 was not declared. Should it be static?
The const was also missing.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: Ibb5cfaf67ac980bf0af27712a95dbef05b617c25
diff --git a/drivers/st/pmic/stm32mp_pmic.c b/drivers/st/pmic/stm32mp_pmic.c
index 0139661..7030cf5 100644
--- a/drivers/st/pmic/stm32mp_pmic.c
+++ b/drivers/st/pmic/stm32mp_pmic.c
@@ -403,7 +403,7 @@
 	}
 }
 
-struct regul_ops pmic_ops = {
+static const struct regul_ops pmic_ops = {
 	.set_state = pmic_set_state,
 	.get_state = pmic_get_state,
 	.set_voltage = pmic_set_voltage,