Correct SPL uses of CMD_FDT

This converts 2 usages of this option to the non-SPL form, since there is
no SPL_CMD_FDT defined in Kconfig

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/boot/bootm.c b/boot/bootm.c
index 56b82bb..2eec60e 100644
--- a/boot/bootm.c
+++ b/boot/bootm.c
@@ -313,7 +313,7 @@
 		return 1;
 	}
 
-	if (CONFIG_IS_ENABLED(CMD_FDT))
+	if (IS_ENABLED(CONFIG_CMD_FDT))
 		set_working_fdt_addr(map_to_sysmem(images.ft_addr));
 #endif