dma-buf: fix timeout handling in dma_resv_wait_timeout v2

Even the kerneldoc says that with a zero timeout the function should not
wait for anything, but still return 1 to indicate that the fences are
signaled now.

Unfortunately that isn't what was implemented, instead of only returning
1 we also waited for at least one jiffies.

Fix that by adjusting the handling to what the function is actually
documented to do.

v2: improve code readability

Reported-by: Marek Olšák <[e-mail]>
Reported-by: Lucas Stach <[e-mail]>
Signed-off-by: Christian König <[e-mail]>
Reviewed-by: Lucas Stach <[e-mail]>
Cc: <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

drivers/dma-buf/dma-resv.c

···
 	dma_resv_iter_begin(&cursor, obj, usage);
 	dma_resv_for_each_fence_unlocked(&cursor, fence) {
 
-		ret = dma_fence_wait_timeout(fence, intr, ret);
-		if (ret <= 0) {
-			dma_resv_iter_end(&cursor);
-			return ret;
-		}
+		ret = dma_fence_wait_timeout(fence, intr, timeout);
+		if (ret <= 0)
+			break;
+
+		/* Even for zero timeout the return value is 1 */
+		if (timeout)
+			timeout = ret;
 	}
 	dma_resv_iter_end(&cursor);