drivers: ipmi: Drop device reference

Drop the reference to a device found via bus_find_device()

Cc: Corey Minyard <minyard@acm.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Message-Id: <1559577023-558-3-git-send-email-suzuki.poulose@arm.com>
[Moved the put_device() to after the platform_device_unregister(), for
 better style.]
Signed-off-by: Corey Minyard <cminyard@mvista.com>