drm/i915: Tidy awaiting on dma-fences

Just tidy up the return handling for completed dma-fences. While it may
return errors for invalid fence, we already know that we have a good
fence and the only error will be an already signaled fence.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200511075722.13483-5-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_sw_fence.c

@@ -546,12 +546,10 @@ int __i915_sw_fence_await_dma_fence(struct i915_sw_fence *fence,
 	cb->fence = fence;
 	i915_sw_fence_await(fence);
 
-	ret = dma_fence_add_callback(dma, &cb->base, __dma_i915_sw_fence_wake);
-	if (ret == 0) {
 	ret = 1;
-	} else {
+	if (dma_fence_add_callback(dma, &cb->base, __dma_i915_sw_fence_wake)) {
+		/* fence already signaled */
 		__dma_i915_sw_fence_wake(dma, &cb->base);
-		if (ret == -ENOENT) /* fence already signaled */
 		ret = 0;
 	}