stm32mp: stm32prog: support empty flashlayout

When the STM32CubeProgrammer sent a empty flashlayout.tsv
file, the command stm32prog correctly parse the file
but data->dev_nb = 0 and the stm32prog_devices_init
operations should be skipped.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/mach-stm32mp/cmd_stm32prog/stm32prog.c b/arch/arm/mach-stm32mp/cmd_stm32prog/stm32prog.c
index a720d0b..7067605 100644
--- a/arch/arm/mach-stm32mp/cmd_stm32prog/stm32prog.c
+++ b/arch/arm/mach-stm32mp/cmd_stm32prog/stm32prog.c
@@ -1884,6 +1884,10 @@
 	if (ret)
 		goto error;
 
+	/* empty flashlayout */
+	if (!data->dev_nb)
+		return;
+
 	/* initialize the selected device */
 	for (i = 0; i < data->dev_nb; i++) {
 		ret = init_device(data, &data->dev[i]);