scsi: aic7xxx: aic79xx: mark expected switch fall-through

In preparation to enabling -Wimplicit-fallthrough, mark switch cases where
we are expecting to fall through.

Notice that, in some cases, I replaced "FALLTHROUGH" with a "fall through"
annotation and then placed it at the bottom of the corresponding switch
case, which is what GCC is expecting to find.

Addresses-Coverity-ID: 114961 ("Missing break in switch")
Addresses-Coverity-ID: 114962 ("Missing break in switch")
Addresses-Coverity-ID: 114963 ("Missing break in switch")
Addresses-Coverity-ID: 114964 ("Missing break in switch")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Hannes Reinecke <hare@suse.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>