bionic: Correct \r at the end of puts()

Since puts() calls serial_putc() directly, it needs to supply its own
\r before \n.

Signed-off-by: Sean Cross <xobs@kosagi.com>

bionic.c

@@ -345,6 +345,7 @@ void _msleep(uint32_t msecs)
 int puts(const char *str)
 {
 	serial_puts(str);
+	serial_putc('\r');
 	serial_putc('\n');
 	return 1;
 }