mei: Fix comments in drivers/misc/mei

Correct typos and fix stray comments.

Signed-off-by: Masanari Iida <standby24x7@gmail.com>
Acked-by: Winkler, Tomas <tomas.winkler@intel.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>