rtc-at91sam9: Correct size given to memset

Memset should be given the size of the structure, not the size of the
pointer.

The semantic patch that makes this change is as follows:
(http://coccinelle.lip6.fr/)

// <smpl>
@@
type T;
T *x;
expression E;
@@

memset(x, E, sizeof(
+ *
 x))
// </smpl>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Alessandro Zummo <a.zummo@towertech.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/rtc/rtc-at91sam9.c

@@ -161,7 +161,7 @@ static int at91_rtc_readalarm(struct device *dev, struct rtc_wkalrm *alrm)
 	if (offset == 0)
 		return -EILSEQ;
 
-	memset(alrm, 0, sizeof(alrm));
+	memset(alrm, 0, sizeof(*alrm));
 	if (alarm != ALARM_DISABLED && offset != 0) {
 		rtc_time_to_tm(offset + alarm, tm);