env: Adjust the load() method to return an error

The load() methods have inconsistent behaviour on error. Some of them load
an empty default environment. Some load an environment containing an error
message. Others do nothing.

As a step in the right direction, have the method return an error code.
Then the caller could handle this itself in a consistent way.

Signed-off-by: Simon Glass <sjg@chromium.org>

env/nvram.c

@@ -51,7 +51,7 @@ static int env_nvram_get_char(int index)
 }
 #endif
 
-static void env_nvram_load(void)
+static int env_nvram_load(void)
 {
 	char buf[CONFIG_ENV_SIZE];
 
@@ -61,6 +61,8 @@ static void env_nvram_load(void)
 	memcpy(buf, (void *)CONFIG_ENV_ADDR, CONFIG_ENV_SIZE);
 #endif
 	env_import(buf, 1);
+
+	return 0;
 }
 
 static int env_nvram_save(void)