ipmi: Fix multi-part message handling

Lots of little fixes for multi-part messages:

The values was not being re-initialized, if something went wrong
handling a multi-part message and it got left in a bad state, it
might be an issue.

The commands were not correct when issuing multi-part reads, the
code was not passing in the proper value for commands.  Also clean
up some minor formatting issues.

Get the block number from the right location, limit the maximum send
message size to 63 bytes and explain why, and fix some minor sylistic
issues.

Signed-off-by: Corey Minyard <cminyard@mvista.com>