[U-Boot] env_mmc: Fix broken build due to set_default_env() change

[Steve Sakoman]

Previously the function was set_default_env(void), it is now
set_default_env(const char *s). This patch adds the required
parameter. This fixes a broken build on OMAP4430 SDP.

Signed-off-by: Steve Sakoman <steve.sakoman at linaro.org>
---

diff --git a/common/env_mmc.c b/common/env_mmc.c
index 14203b6..cc288d4 100644
--- a/common/env_mmc.c
+++ b/common/env_mmc.c
@@ -147,7 +147,6 @@ void env_relocate_spec(void)
 #if !defined(ENV_IS_EMBEDDED)
 static void use_default()
 {
-	puts ("*** Warning - bad CRC or MMC, using default environment\n\n");
-	set_default_env();
+	set_default_env(NULL);
 }
 #endif