rename _end to __bss_end__

Currently, _end is used for end of BSS section.  We want _end to mean
end of u-boot image, so we rename _end to __bss_end__ first.

Signed-off-by: Po-Yu Chuang <ratbert@faraday-tech.com>
diff --git a/examples/standalone/stubs.c b/examples/standalone/stubs.c
index 2d2e709..1379df7 100644
--- a/examples/standalone/stubs.c
+++ b/examples/standalone/stubs.c
@@ -187,14 +187,14 @@
 #include <_exports.h>
 }
 
-extern unsigned long __bss_start, _end;
+extern unsigned long __bss_start, __bss_end__;
 
 void app_startup(char * const *argv)
 {
 	unsigned char * cp = (unsigned char *) &__bss_start;
 
 	/* Zero out BSS */
-	while (cp < (unsigned char *)&_end) {
+	while (cp < (unsigned char *)&__bss_end__) {
 		*cp++ = 0;
 	}