initialize struct sigevent before timer_create

When qemu is run under valgrind, valgrind shows the following output
on exit:

==3648== 1 errors in context 2 of 2:
==3648== Syscall param timer_create(evp) points to uninitialised byte(s)
==3648==    at 0x54E936A: timer_create (in /lib/librt-2.9.so)
==3648==    by 0x405DCF: dynticks_start_timer (vl.c:1549)
==3648==    by 0x40A966: main (vl.c:1726)
==3648==  Address 0x7fefffb34 is on thread 1's stack
==3648==  Uninitialised value was created by a stack allocation
==3648==    at 0x405D60: dynticks_start_timer (vl.c:1534)

This patch is a simple fix to remove this potential problem.
Signed-off-by: NJean-Christophe DUBOIS <jcd@tribudubois.net>

vl.c

@@ -1542,6 +1542,11 @@ static int dynticks_start_timer(struct qemu_alarm_timer *t)
 
     sigaction(SIGALRM, &act, NULL);
 
+    /* 
+     * Initialize ev struct to 0 to avoid valgrind complaining
+     * about uninitialized data in timer_create call
+     */
+    memset(&ev, 0, sizeof(ev));
     ev.sigev_value.sival_int = 0;
     ev.sigev_notify = SIGEV_SIGNAL;
     ev.sigev_signo = SIGALRM;