allow the rb kernel to call uartenable directly

Reference: /n/atom/patch/applied2013/uartenable
Date: Wed Jul 31 20:58:09 CES 2013
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/devuart.c	Wed Jul 31 20:57:47 2013
+++ /sys/src/9/port/devuart.c	Wed Jul 31 20:57:48 2013
@@ -45,7 +45,7 @@
 /*
  *  enable/disable uart and add/remove to list of enabled uarts
  */
-static Uart*
+Uart*
 uartenable(Uart *p)
 {
 	int opened;