ARM: stm32mp: skip ft_system_setup when the soc node is absent

The function ft_system_setup shouldn't return an error when the
/soc node is absent in the provided device tree but just skip the
updates.

This patch solves an issue when the U-Boot pytest is executed on board.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/mach-stm32mp/fdt.c b/arch/arm/mach-stm32mp/fdt.c
index 91330a6..b1a4b76 100644
--- a/arch/arm/mach-stm32mp/fdt.c
+++ b/arch/arm/mach-stm32mp/fdt.c
@@ -260,6 +260,9 @@
 	char name[SOC_NAME_SIZE];
 
 	soc = fdt_path_offset(blob, "/soc");
+	/* when absent, nothing to do */
+	if (soc == -FDT_ERR_NOTFOUND)
+		return 0;
 	if (soc < 0)
 		return soc;