fix(drivers/st/pmic): missing error check

In pmic_operate(), "regulators" node value must be checked before
entering in the fdt_for_each_subnode loop.

Change-Id: I1460cd24ec56ec47ab644f396b71b92973e75fb4
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@st.com>
Signed-off-by: Yann Gautier <yann.gautier@st.com>

drivers/st/pmic/stm32mp_pmic.c

@@ -121,6 +121,9 @@ int dt_pmic_configure_boot_on_regulators(void)
 	}
 
 	regulators_node = fdt_subnode_offset(fdt, pmic_node, "regulators");
+	if (regulators_node < 0) {
+		return -ENOENT;
+	}
 
 	fdt_for_each_subnode(regulator_node, fdt, regulators_node) {
 		const fdt32_t *cuint;