a3m071: Make spl_start_uboot test like getenv_yesno does

This change makes the behaviour slightly more rebust and will match
other implementations which can use getenv_yesno directly.

Acked-by: Stefan Roese <sr@denx.de>
Signed-off-by: Tom Rini <trini@ti.com>
diff --git a/board/a3m071/a3m071.c b/board/a3m071/a3m071.c
index 7aeefb2..b96ba81 100644
--- a/board/a3m071/a3m071.c
+++ b/board/a3m071/a3m071.c
@@ -412,7 +412,8 @@
 
 	env_init();
 	getenv_f("boot_os", s, sizeof(s));
-	if ((s != NULL) && (strcmp(s, "yes") == 0))
+	if ((s != NULL) && (*s == '1' || *s == 'y' || *s == 'Y' ||
+			    *s == 't' || *s == 'T'))
 		return 0;
 
 	return 1;