serial: sandbox: optimize puts

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/serial/sandbox.c b/drivers/serial/sandbox.c
index 0d65587..cae6c94 100644
--- a/drivers/serial/sandbox.c
+++ b/drivers/serial/sandbox.c
@@ -44,8 +44,7 @@
 
 void serial_puts(const char *str)
 {
-	while (*str)
-		serial_putc(*str++);
+	os_write(1, str, strlen(str));
 }
 
 int serial_getc(void)