drivers: qcom: rpmh: Do not return on error while sending

It is possible that while sending multiples of requests using passthru
API. Do not return from the API, since some requests might have gone
through. We need to wait for them.

Clean up prior rpm_msg objects, if the request from pool fails.

Change-Id: I3ea43d3605f028e2653cd5a18bd3cc685cf14234
Signed-off-by: Lina Iyer <ilina@codeaurora.org>