Correct SPL use of CMD_STM32PROG

This converts 1 usage of this option to the non-SPL form, since there is
no SPL_CMD_STM32PROG defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/board/st/common/stm32mp_mtdparts.c b/board/st/common/stm32mp_mtdparts.c
index 1887842..67a56a2 100644
--- a/board/st/common/stm32mp_mtdparts.c
+++ b/board/st/common/stm32mp_mtdparts.c
@@ -96,7 +96,7 @@
 	case BOOT_SERIAL_UART:
 	case BOOT_SERIAL_USB:
 		serial = true;
-		if (CONFIG_IS_ENABLED(CMD_STM32PROG)) {
+		if (IS_ENABLED(CONFIG_CMD_STM32PROG)) {
 #ifdef CONFIG_STM32MP15x_STM32IMAGE
 			tee = stm32prog_get_tee_partitions();
 #endif