tools/mxsimage: Remove fclose on empty FILE pointer

If `sb_load_cmdfile()` fails to open the configuration file it will jump
to error handling where the code will try to `fclose()` the FILE pointer
which is NULL causing `mkimage` to segfault.

This patch removes the label for error handling and instead returns
immediately which skips the `fclose()` and prevents the segfault. The
errno is also described in the error message to guide users.

Signed-off-by: Mattias Hansson <hansson.mattias@gmail.com>
Reviewed-by: Wolfgang Denk <wd@denx.de>
diff --git a/tools/mxsimage.c b/tools/mxsimage.c
index 002f4b5..fee022a 100644
--- a/tools/mxsimage.c
+++ b/tools/mxsimage.c
@@ -1595,8 +1595,11 @@
 	size_t len;
 
 	fp = fopen(ictx->cfg_filename, "r");
-	if (!fp)
-		goto err_file;
+	if (!fp) {
+		fprintf(stderr, "ERR: Failed to load file \"%s\": \"%s\"\n",
+			ictx->cfg_filename, strerror(errno));
+		return -EINVAL;
+	}
 
 	while ((rlen = getline(&line, &len, fp)) > 0) {
 		memset(&cmd, 0, sizeof(cmd));
@@ -1616,12 +1619,6 @@
 	fclose(fp);
 
 	return 0;
-
-err_file:
-	fclose(fp);
-	fprintf(stderr, "ERR: Failed to load file \"%s\"\n",
-		ictx->cfg_filename);
-	return -EINVAL;
 }
 
 static int sb_build_tree_from_cfg(struct sb_image_ctx *ictx)