libvhost-user: Change dev->postcopy_ufd assignment to make it C90 compliant

The assignment of dev->postcopy_ufd can be moved into an else clause and
then the code becomes C90 compliant.

  CC       libvhost-user.o
libvhost-user.c: In function ‘vu_set_postcopy_advise’:
libvhost-user.c:1625:5: error: ISO C90 forbids mixed declarations and code [-Werror=declaration-after-statement]
 1625 |     struct uffdio_api api_struct;
      |     ^~~~~~

Understandable, it might be desired to avoid else clauses, but in this
case it seems clear enough and frankly the dev->postcopy_ufd is only
assigned once.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <74db52afb1203c4580ffc7fa462b4b2ba260a353.1671741278.git.marcel@holtmann.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

subprojects/libvhost-user/libvhost-user.c

@@ -1599,12 +1599,13 @@ vu_set_config(VuDev *dev, VhostUserMsg *vmsg)
 static bool
 vu_set_postcopy_advise(VuDev *dev, VhostUserMsg *vmsg)
 {
-    dev->postcopy_ufd = -1;
 #ifdef UFFDIO_API
     struct uffdio_api api_struct;
 
     dev->postcopy_ufd = syscall(__NR_userfaultfd, O_CLOEXEC | O_NONBLOCK);
     vmsg->size = 0;
+#else
+    dev->postcopy_ufd = -1;
 #endif
 
     if (dev->postcopy_ufd == -1) {