drm/msm: fix return value check in _msm_gem_kernel_new()

In case of error, the function msm_gem_get_vaddr() returns ERR_PTR()
and never returns NULL. The NULL test in the return value check should
be replaced with IS_ERR().

Fixes: 8223286d62e2 ("drm/msm: Add a helper function for in-kernel
buffer allocations")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Rob Clark <robdclark@gmail.com>

drivers/gpu/drm/msm/msm_gem.c

@@ -1045,10 +1045,10 @@ static void *_msm_gem_kernel_new(struct drm_device *dev, uint32_t size,
 	}
 
 	vaddr = msm_gem_get_vaddr(obj);
-	if (!vaddr) {
+	if (IS_ERR(vaddr)) {
 		msm_gem_put_iova(obj, aspace);
 		drm_gem_object_unreference(obj);
-		return ERR_PTR(-ENOMEM);
+		return ERR_CAST(vaddr);
 	}
 
 	if (bo)