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>
diff --git a/env/eeprom.c b/env/eeprom.c
index fbe4fd4..08ef630 100644
--- a/env/eeprom.c
+++ b/env/eeprom.c
@@ -76,7 +76,7 @@
 	return c;
 }
 
-static void env_eeprom_load(void)
+static int env_eeprom_load(void)
 {
 	char buf_env[CONFIG_ENV_SIZE];
 	unsigned int off = CONFIG_ENV_OFFSET;
@@ -182,6 +182,8 @@
 		off, (uchar *)buf_env, CONFIG_ENV_SIZE);
 
 	env_import(buf_env, 1);
+
+	return 0;
 }
 
 static int env_eeprom_save(void)