scsi: esas2r: esas2r_init: mark expected switch fall-throughs

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

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Acked-by: Bradley Grove <bgrove@atto.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>