arm_scmi: cleanup the mailbox channels upon errors

During probe failure current implementation returns with
error without cleaning the mailbox channels.
Update the probe function to cleanup the mail box
channels for scmi tx and rx paths.

Change-Id: Iafd370638cad586c47ff8191ed12a0933bf4dbf3
Signed-off-by: Santosh Mardi <gsantosh@codeaurora.org>