i5000-edac: hold reference to mci kobject

It turns out that edac_mc_del_mc will kobject_put the last kref on the
mci object.

If the timing is just right, that means that the mci object is freed
before before i5000_remove_one has a chance to free the resources
associated with it, causing a null pointer exceptions when unloading the
driver.  Insert a kobject_{get,put} pair so that this doesn't happen.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Cc: Doug Thompson <norsk5@yahoo.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>