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 <marek.olsak@amd.com>
Reported-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20250129105841.1806-1-christian.koenig@amd.com