correct setmalloctag

Reference: /n/atom/patch/applied/9allocnit
Date: Wed Sep  9 07:21:18 CES 2015
Signed-off-by: quanstro@quanstro.net

--- /sys/src/9/port/alloc.c	Wed Sep  9 07:21:10 2015
+++ /sys/src/9/port/alloc.c	Wed Sep  9 07:21:11 2015
@@ -275,7 +275,7 @@
 	return v;
 }
 
-uintptr
+void
 setmalloctag(void *v, uintptr pc)
 {
 	ulong *u;