Makefile: add -m32 by default

It is not harmful to specify -m32 always.

Signed-off-by: Alek Du <alek.du@intel.com>
diff --git a/Makefile b/Makefile
index a2c0301..dcbb212 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,5 @@
 OBJ=bootstub.o spi-uart.o head.o sfi.o
-CFLAGS=-ffreestanding -Wall
-#for cross compile
-#CFLAGS=-m32 -ffreestanding -Wall
+CFLAGS=-m32 -ffreestanding -Wall
 
 all: bootstub