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
1 file changed