tee: fix memory allocation failure checks on drv_data and amdtee

Currently the memory allocation failure checks on drv_data and
amdtee are using IS_ERR rather than checking for a null pointer.
Fix these checks to use the conventional null pointer check.

Addresses-Coverity: ("Dereference null return")
Fixes: 757cc3e9 ("tee: add AMD-TEE driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Rijo Thomas <Rijo-john.Thomas@amd.com>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/tee/amdtee/core.c

@@ -446,11 +446,11 @@ static int __init amdtee_driver_init(void)
 	}
 
 	drv_data = kzalloc(sizeof(*drv_data), GFP_KERNEL);
-	if (IS_ERR(drv_data))
+	if (!drv_data)
 		return -ENOMEM;
 
 	amdtee = kzalloc(sizeof(*amdtee), GFP_KERNEL);
-	if (IS_ERR(amdtee)) {
+	if (!amdtee) {
 		rc = -ENOMEM;
 		goto err_kfree_drv_data;
 	}