scsi/megaraid fixed several typos in comments

Fixed several typos in comments in megaraid_mbox.c, megaraid_mm.c
and megaraid_sas_fusion.h.

Signed-off-by: Matthias Schid <aircrach115@gmail.com>
Signed-off-by: Stefan Huber <steffhip@gmail.com>
Signed-off-by: Simon Puels <simon.puels@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>