Fix incorrect use of getenv() before relocation

A large number of boards incorrectly used getenv() in their board init
code running before relocation.  In some cases this caused U-Boot to
hang when certain environment variables grew too long.
Fix the code to use getenv_r().

Signed-off-by: Wolfgang Denk <wd@denx.de>
Cc: Stefan Roese <sr@denx.de>
Cc: The LEOX team <team@leox.org>
Cc: Michael Schwingen <michael@schwingen.org>
Cc: Georg Schardt <schardt@team-ctech.de>
Cc: Werner Pfister <Pfister_Werner@intercontrol.de>
Cc: Dirk Eibach <eibach@gdsys.de>
Cc: Peter De Schrijver <p2@mind.be>
Cc: John Zhan <zhanz@sinovee.com>
Cc: Rishi Bhattacharya <rishi@ti.com>
Cc: Peter Tyser <ptyser@xes-inc.com>
diff --git a/board/amcc/taishan/taishan.c b/board/amcc/taishan/taishan.c
index 2957a77..fcaf7fd 100644
--- a/board/amcc/taishan/taishan.c
+++ b/board/amcc/taishan/taishan.c
@@ -193,12 +193,13 @@
 
 int checkboard (void)
 {
-	char *s = getenv ("serial#");
+	char buf[64];
+	int i = getenv_f("serial#", buf, sizeof(buf));
 
 	printf ("Board: Taishan - AMCC PPC440GX Evaluation Board");
-	if (s != NULL) {
-		puts (", serial# ");
-		puts (s);
+	if (i > 0) {
+		puts(", serial# ");
+		puts(buf);
 	}
 	putc ('\n');