Add cmd_process_error() to report and process errors

U-Boot now uses errors defined in include/errno.h which are negative
integers. Commands which fail need to report the error and return 1
to indicate failure. Add this functionality in cmd_process_error().

For now this merely reports the error number. It would be possible
also to produce a helpful error message by storing the error strings
in U-Boot.

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

common/command.c

@@ -538,3 +538,13 @@ enum command_ret_t cmd_process(int flag, int argc, char * const argv[],
 		rc = cmd_usage(cmdtp);
 	return rc;
 }
+
+int cmd_process_error(cmd_tbl_t *cmdtp, int err)
+{
+	if (err) {
+		printf("Command '%s' failed: Error %d\n", cmdtp->name, err);
+		return 1;
+	}
+
+	return 0;
+}