rpc: Uninitialized pointer read

Initialize *xprt to avoid exposing a random value
in cleanup_svc_vc_create.
This is the kernel counterpart of r278041.

CID:		1007340

sys/rpc/svc_vc.c

@@ -143,7 +143,7 @@ SVCXPRT *
 svc_vc_create(SVCPOOL *pool, struct socket *so, size_t sendsize,
     size_t recvsize)
 {
-	SVCXPRT *xprt;
+	SVCXPRT *xprt = NULL;
 	struct sockaddr* sa;
 	int error;