correct signature in comment

Reference: /n/atom/patch/applied/monmwaitsig
Date: Mon May  5 21:35:42 CES 2014
Signed-off-by: quanstro@quanstro.net

--- /sys/src/nix/k10/l64v.s	Mon May  5 21:35:42 2014
+++ /sys/src/nix/k10/l64v.s	Mon May  5 21:35:42 2014
@@ -379,7 +379,7 @@
 #define MWAIT		BYTE $0x0f; BYTE $0x01; BYTE $0xc9
 
 /*
- * u64int monmwait(u64int*, u64int)
+ * uintptr monmwait(void*, uintptr)
  */
 TEXT	k10monmwait64(SB),1,$16
 	MOVQ	val+8(FP), BX