explain issue better

Reference: /n/atom/patch/applied/usbohciblockick
Date: Mon May  5 21:34:32 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/usbohci.c	Mon May  5 21:34:32 2014
+++ /sys/src/nix/k10/usbohci.c	Mon May  5 21:34:32 2014
@@ -449,8 +449,9 @@
 }
 
 /*
- * allocb may use memory outside the normal malloc arena
- * this is so gross.
+ * allocb may use memory outside the normal malloc arena,
+ * and therefore above 4G.  this is quite gross, and probablly
+ * not even an appropriate use for a Block*.
  */
 static Block*
 loallocb(int size)