test on wrong function pointer.

Reference: /n/atom/patch/applied/putctest
Date: Sun Jan  5 16:18:04 CET 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/port/devuart.c	Sun Jan  5 16:17:56 2014
+++ /sys/src/nix/port/devuart.c	Sun Jan  5 16:17:57 2014
@@ -865,7 +865,7 @@
 	char *e;
 	Uart *u;
 
-	if((u = consuart) == nil || u->phys->getc == nil)
+	if((u = consuart) == nil || u->phys->putc == nil)
 		return;
 
 	e = s+n;