fix(stm32mp1): rework switch/case for MISRA

Avoid the use of return inside switch/case in stm32mp_is_single_core().
Although this MISRA rulre might not be enforced, we align on what is done
for stm32mp_is_auth_supported().

Change-Id: I00a5ec1b18c55b4254af00c9c5cf5a4dce104175
Signed-off-by: Yann Gautier <yann.gautier@st.com>
diff --git a/plat/st/stm32mp1/stm32mp1_private.c b/plat/st/stm32mp1/stm32mp1_private.c
index 5156975..9b39b9d 100644
--- a/plat/st/stm32mp1/stm32mp1_private.c
+++ b/plat/st/stm32mp1/stm32mp1_private.c
@@ -420,15 +420,20 @@
 /* Return true when SoC provides a single Cortex-A7 core, and false otherwise */
 bool stm32mp_is_single_core(void)
 {
+	bool single_core = false;
+
 	switch (get_part_number()) {
 	case STM32MP151A_PART_NB:
 	case STM32MP151C_PART_NB:
 	case STM32MP151D_PART_NB:
 	case STM32MP151F_PART_NB:
-		return true;
+		single_core = true;
+		break;
 	default:
-		return false;
+		break;
 	}
+
+	return single_core;
 }
 
 /* Return true when device is in closed state */