ipmi: kcs_bmc: Enable IBF on open

This way devices don't get delivered IRQs when no-one is interested.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Message-Id: <20210608104757.582199-11-andrew@aj.id.au>
Signed-off-by: Corey Minyard <cminyard@mvista.com>