virgl: Fix unused var warnings in release build from assertions.

Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6462>
diff --git a/src/gallium/winsys/virgl/vtest/virgl_vtest_socket.c b/src/gallium/winsys/virgl/vtest/virgl_vtest_socket.c
index 463bff0..f24116e 100644
--- a/src/gallium/winsys/virgl/vtest/virgl_vtest_socket.c
+++ b/src/gallium/winsys/virgl/vtest/virgl_vtest_socket.c
@@ -148,7 +148,7 @@
    uint32_t version_buf[VCMD_PROTOCOL_VERSION_SIZE];
    uint32_t busy_wait_buf[VCMD_BUSY_WAIT_SIZE];
    uint32_t busy_wait_result[1];
-   int ret;
+   ASSERTED int ret;
 
    vtest_hdr[VTEST_CMD_LEN] = VCMD_PING_PROTOCOL_VERSION_SIZE;
    vtest_hdr[VTEST_CMD_ID] = VCMD_PING_PROTOCOL_VERSION;
@@ -521,7 +521,7 @@
    uint32_t vtest_hdr[VTEST_HDR_SIZE];
    uint32_t cmd[VCMD_BUSY_WAIT_SIZE];
    uint32_t result[1];
-   int ret;
+   ASSERTED int ret;
    vtest_hdr[VTEST_CMD_LEN] = VCMD_BUSY_WAIT_SIZE;
    vtest_hdr[VTEST_CMD_ID] = VCMD_RESOURCE_BUSY_WAIT;
    cmd[VCMD_BUSY_WAIT_HANDLE] = handle;