configure: Fix compiler warning in config.log (value was never used)

Signed-off-by: Stefan Weil <[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>
diff --git a/configure b/configure
index e9725d4..bd6f10f 100755
--- a/configure
+++ b/configure
@@ -2269,8 +2269,7 @@
 
 int main(void)
 {
-    int efd = eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
-    return 0;
+    return eventfd(0, EFD_NONBLOCK | EFD_CLOEXEC);
 }
 EOF
 if compile_prog "" "" ; then