Makefile: Fix CONFIG_SYS_UBOOT_START default value

This patches restores boot on boards which rely on
CONFIG_SYS_UBOOT_START equal to CONFIG_SYS_TEXT_BASE when using SPL

Fixes: d3e97b53c1f2 ("spl: fix entry_point equal to load_addr")

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/Makefile b/Makefile
index 6f62d76..cc126eb 100644
--- a/Makefile
+++ b/Makefile
@@ -1265,7 +1265,7 @@
 # from the SPL U-Boot version.
 #
 ifndef CONFIG_SYS_UBOOT_START
-CONFIG_SYS_UBOOT_START := 0
+CONFIG_SYS_UBOOT_START := $(CONFIG_SYS_TEXT_BASE)
 endif
 
 # Boards with more complex image requirements can provide an .its source file