staging: lustre: fix return value check in capa_hmac()

In case of error, the function crypto_alloc_hash() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check
should be replaced with IS_ERR().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/lustre/lustre/obdclass/capa.c

@@ -272,10 +272,10 @@ int capa_hmac(__u8 *hmac, struct lustre_capa *capa, __u8 *key)
 	alg = &capa_hmac_algs[capa_alg(capa)];
 
 	tfm = crypto_alloc_hash(alg->ha_name, 0, 0);
-	if (!tfm) {
+	if (IS_ERR(tfm)) {
 		CERROR("crypto_alloc_tfm failed, check whether your kernel"
 		       "has crypto support!\n");
-		return -ENOMEM;
+		return PTR_ERR(tfm);
 	}
 	keylen = alg->ha_keylen;