fix(stm32mp1): add const for strings in stm32mp_get_soc_name()

This corrects MISRA C2012-7.4:
A string literal shall not be assigned to an object unless the object's
type is "pointer to const-qualified char".

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I0c9f483dce9abd32647d5f5e2df72047cdd376dd
diff --git a/plat/st/stm32mp1/stm32mp1_private.c b/plat/st/stm32mp1/stm32mp1_private.c
index ae39c0b..e6cb071 100644
--- a/plat/st/stm32mp1/stm32mp1_private.c
+++ b/plat/st/stm32mp1/stm32mp1_private.c
@@ -378,7 +378,7 @@
 
 void stm32mp_get_soc_name(char name[STM32_SOC_NAME_SIZE])
 {
-	char *cpu_s, *cpu_r, *pkg;
+	const char *cpu_s, *cpu_r, *pkg;
 
 	/* MPUs Part Numbers */
 	switch (get_part_number()) {