env: add the same prefix to error messages to make it detectable by tests

The error message should start with `## Error: ` so that it's easily
detectable by tests without needing to have a complex regexp for
matching all possible error message patterns.

Let's add the `## Error: ` prefix to the error messages since it's the
one already in use.

Suggested-by: Stephen Warren <swarren@wwwdotorg.org>
Signed-off-by: Quentin Schulz <quentin.schulz@bootlin.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Stephen Warren <swarren@nvidia.com>
Tested-by: Stephen Warren <swarren@nvidia.com>
diff --git a/env/common.c b/env/common.c
index 1430100..3317cef 100644
--- a/env/common.c
+++ b/env/common.c
@@ -79,7 +79,8 @@
 	if (himport_r(&env_htab, (char *)default_environment,
 			sizeof(default_environment), '\0', flags, 0,
 			0, NULL) == 0)
-		pr_err("Environment import failed: errno = %d\n", errno);
+		pr_err("## Error: Environment import failed: errno = %d\n",
+		       errno);
 
 	gd->flags |= GD_FLG_ENV_READY;
 	gd->flags |= GD_FLG_ENV_DEFAULT;