fix code typo


git-svn-id: svn://svn.valgrind.org/valgrind/trunk@2249 a5019735-40e9-0310-863c-91ae7b9d1cf9
diff --git a/coregrind/vg_syscalls.c b/coregrind/vg_syscalls.c
index f1509ad..48db207 100644
--- a/coregrind/vg_syscalls.c
+++ b/coregrind/vg_syscalls.c
@@ -4131,7 +4131,7 @@
 			a1/8 /* __FD_SETSIZE/8 */ );
       if (a3 != (Addr)NULL)
 	 SYSCALL_TRACK( pre_mem_read, tid, "select(writefds)", a3, 
-			arg1/8 /* __FD_SETSIZE/8 */ );
+			a1/8 /* __FD_SETSIZE/8 */ );
       if (a4 != (Addr)NULL)
 	 SYSCALL_TRACK( pre_mem_read, tid, "select(exceptfds)", a4, 
 			a1/8 /* __FD_SETSIZE/8 */ );