msm: rpm-smd: Fix race conditions with SMP

When a rpm message is sent in a noirq context from Core 1, it is
possible that the ack is processed by Core 0. This would result in
the ack not getting propageted correctly to the client. Also, added a
check on error codes from a smd API.

Change-Id: Id983dc50ad85dfef8fe6971c4e5eda2e77f24d2b
Signed-off-by: Mahesh Sivasubramanian <msivasub@codeaurora.org>