libvhost-user: Switch to unsigned int for inuse field in struct VuVirtq

It seems there is no need to keep the inuse field signed and end up with
compiler warnings for sign-compare.

  CC       libvhost-user.o
libvhost-user.c: In function ‘vu_queue_pop’:
libvhost-user.c:2763:19: error: comparison of integer expressions of different signedness: ‘int’ and ‘unsigned int’ [-Werror=sign-compare]
 2763 |     if (vq->inuse >= vq->vring.num) {
      |                   ^~
libvhost-user.c: In function ‘vu_queue_rewind’:
libvhost-user.c:2808:13: error: comparison of integer expressions of different signedness: ‘unsigned int’ and ‘int’ [-Werror=sign-compare]
 2808 |     if (num > vq->inuse) {
      |             ^

Instead of casting the comparision to unsigned int, just make the inuse
field unsigned int in the fist place.

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Message-Id: <20221219175337.377435-8-marcel@holtmann.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

subprojects/libvhost-user/libvhost-user.h

@@ -343,7 +343,7 @@ typedef struct VuVirtq {
     /* Notification enabled? */
     bool notification;
 
-    int inuse;
+    unsigned int inuse;
 
     vu_queue_handler_cb handler;