libvhost-user: Include poll.h instead of sys/poll.h

Musl libc complains about it's wrong usage.

In file included from ../subprojects/libvhost-user/libvhost-user.h:20,
                 from ../subprojects/libvhost-user/libvhost-user-glib.h:19,
                 from ../subprojects/libvhost-user/libvhost-user-glib.c:15:
/usr/include/sys/poll.h:1:2: error: #warning redirecting incorrect #include <sys/poll.h> to <poll.h> [-Werror=cpp]
    1 | #warning redirecting incorrect #include <sys/poll.h> to <poll.h>
      |  ^~~~~~~

Signed-off-by: Jiaxun Yang <[email protected]>
Reviewed-by: Thomas Huth <[email protected]>
Reviewed-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <[email protected]>
Signed-off-by: Thomas Huth <[email protected]>

Author: FlyGoat

subprojects/libvhost-user/libvhost-user.h

@@ -17,7 +17,7 @@
 #include <stdint.h>
 #include <stdbool.h>
 #include <stddef.h>
-#include <sys/poll.h>
+#include <poll.h>
 #include <linux/vhost.h>
 #include <pthread.h>
 #include "standard-headers/linux/virtio_ring.h"