nds32: Fix compile error.

Fix compile error with gcc 4.9.3

Signed-off-by: rick <rick@andestech.com>
Cc: Andes <uboot@andestech.com>
diff --git a/arch/nds32/cpu/n1213/start.S b/arch/nds32/cpu/n1213/start.S
index 2f0b76c..8b7f8f4 100644
--- a/arch/nds32/cpu/n1213/start.S
+++ b/arch/nds32/cpu/n1213/start.S
@@ -400,7 +400,7 @@
 	! FIXME: Other way to get PC?
 	! FIXME: Update according to the newest spec!!
 1:
-	la	 $r28, 1
+	li	 $r28, 1
 	push $r28
 	mfsr $r28, PSW			! $PSW
 	push $r28