ipmi: kcs_bmc: coding-style fixes and use new poll type

Many for coding-style fixes, and update the poll API with the new
type '__poll_t', this is new commit from linux-4.16-rc1.

Signed-off-by: Haiyue Wang <haiyue.wang@linux.intel.com>
Signed-off-by: Corey Minyard <cminyard@mvista.com>