firmware: exynos-acpm: check saved RX before bailing out on empty RX queue

When we're polling for responses and get a response that corresponds to
another request, we save the RX data in order to drain the RX queue.

If the response for the current request is not found in the request's
iteration of the queue, or if the queue is empty, we must check whether
the RX data was saved by a previous request when it drained the RX queue.

We failed to check for already saved responses when the queue was empty,
and requests could time out. Check saved RX before bailing out on empty
RX queue.

Fixes: a88927b5 ("firmware: add Exynos ACPM protocol driver")
Reported-by: André Draszik <andre.draszik@linaro.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: André Draszik <andre.draszik@linaro.org>
Tested-by: André Draszik <andre.draszik@linaro.org>
Link: https://lore.kernel.org/r/20250324-acpm-drained-rx-queue-v1-1-577774335151@linaro.org


Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>