ipmi:si: Handle waiting messages when BMC failure detected

ipmi:si: Handle waiting messages when BMC failure detected

If a BMC failure is detected, the current message is returned with an
error.  However, if there was a waiting message, it would not be
handled.

Add a check for the waiting message after handling the current message.

Suggested-by: Guenter Roeck <linux@roeck-us.net>
Reported-by: Rafael J. Wysocki <rafael@kernel.org>
Closes: https://lore.kernel.org/linux-acpi/CAK8fFZ58fidGUCHi5WFX0uoTPzveUUDzT=k=AAm4yWo3bAuCFg@mail.gmail.com/
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>