Replace zed's use of malloc with calloc

When zed allocates memory via malloc(), it typically follows that
with a memset().  However, calloc() implementations can often perform
optimizations when zeroing memory:

https://stackoverflow.com/questions/2688466/why-mallocmemset-is-slower-than-calloc

This commit replaces zed's use of malloc() with calloc().

Signed-off-by: Chris Dunlap <cdunlap@llnl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #2736

cmd/zed/zed_conf.c

@@ -51,12 +51,10 @@ zed_conf_create(void)
 {
 	struct zed_conf *zcp;
 
-	zcp = malloc(sizeof (*zcp));
+	zcp = calloc(1, sizeof (*zcp));
 	if (!zcp)
 		goto nomem;
 
-	memset(zcp, 0, sizeof (*zcp));
-
 	zcp->syslog_facility = LOG_DAEMON;
 	zcp->min_events = ZED_MIN_EVENTS;
 	zcp->max_events = ZED_MAX_EVENTS;