stm32mp1: Fix warnings when compiling with W=1

This patch solves the following warnings:

arch/arm/mach-stm32mp/cpu.c:378:16: warning: comparison between signed
and unsigned integer expressions [-Wsign-compare]
   if (instance > ARRAY_SIZE(serial_addr))
                ^

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Patrick Delaunay <patrick.delaunay@st.com>
1 file changed