cmd: binop: Use new environment api

Since the binop command was introduced, the environment API was changed.
Use the new API to make the command work again.

Signed-off-by: Mario Six <mario.six@gdsys.cc>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/binop.c b/cmd/binop.c
index 787f7a2..be780bf 100644
--- a/cmd/binop.c
+++ b/cmd/binop.c
@@ -26,7 +26,7 @@
 		str_ptr += 2;
 	}
 	*str_ptr = '\0';
-	setenv(varname, str_output);
+	env_set(varname, str_output);
 
 	free(str_output);
 }
@@ -58,7 +58,7 @@
 {
 	char *str_value;
 
-	str_value = getenv(varname);
+	str_value = env_get(varname);
 	if (str_value)
 		decode_hexstring(str_value, result);
 	else