xnvme: Remove unused rc.

Here no need to define a variable only return.

Signed-off-by: yidong0635 <dongx.yi@intel.com>
Change-Id: I6babb8ef94a9b111d5522f1e782cbd095c7da83a
Reviewed-on: https://review.spdk.io/gerrit/c/spdk/spdk/+/14207
Tested-by: SPDK CI Jenkins <sys_sgci@intel.com>
Reviewed-by: Aleksey Marchuk <alexeymar@nvidia.com>
Reviewed-by: Konrad Sztyber <konrad.sztyber@intel.com>
Reviewed-by: Ben Walker <benjamin.walker@intel.com>
Reviewed-by: wanghailiang <hailiangx.e.wang@intel.com>
Reviewed-by: Krzysztof Karas <krzysztof.karas@intel.com>

module/bdev/xnvme/bdev_xnvme.c

@@ -85,13 +85,12 @@ static int
 bdev_xnvme_destruct(void *ctx)
 {
 	struct bdev_xnvme *xnvme = ctx;
-	int rc = 0;
 
 	TAILQ_REMOVE(&g_xnvme_bdev_head, xnvme, link);
 	spdk_io_device_unregister(xnvme, NULL);
 	bdev_xnvme_free(xnvme);
 
-	return rc;
+	return 0;
 }
 
 static void