configure: fix Linux AIO detection

We should set $linux_aio to 'no' if detection failed, otherwise
its contents will be empty, which is a bug as we test for 'yes'
or 'no'.
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>

configure

@@ -1354,6 +1354,7 @@ EOF
     if test "$linux_aio" = "yes" ; then
       feature_not_found "linux AIO"
     fi
+    linux_aio=no
   fi
 fi