ipmi:msghandler: Handle error returns from the SMI sender

ipmi:msghandler: Handle error returns from the SMI sender

It used to be, until recently, that the sender operation on the low
level interfaces would not fail.  That's not the case any more with
recent changes.

So check the return value from the sender operation, and propagate it
back up from there and handle the errors in all places.

Reported-by: Rafael J. Wysocki <rafael@kernel.org>
Fixes: bc3a9d217755 ("ipmi:si: Gracefully handle if the BMC is non-functional")
Cc: stable@vger.kernel.org # 4.18
Signed-off-by: Corey Minyard <corey@minyard.net>
Reviewed-by: Rafael J. Wysocki (Intel) <rafael@kernel.org>