virPerfReadEvent: Prefer saferead over read

Do I really need to explain why?
Well, if read() is interrupted int the middle of reading, we will
never read the rest (even though it's highly unlikely as we are
reading just 8 bytes).

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>

src/util/virperf.c

@@ -247,7 +247,7 @@ virPerfReadEvent(virPerfPtr perf,
     if (event == NULL || !event->enabled)
         return -1;
 
-    if (read(event->fd, value, sizeof(uint64_t)) < 0) {
+    if (saferead(event->fd, value, sizeof(uint64_t)) < 0) {
         virReportSystemError(errno, "%s",
                              _("Unable to read cache data"));
         return -1;