scsi: aic94xx: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding a couple of break and fallthrough statements
instead of just letting the code fall through to the next case.

Link: https://github.com/KSPP/linux/issues/115
Link: https://lore.kernel.org/r/9b58459045d303bbea0160f2e349f5799402a2bf.1605896059.git.gustavoars@kernel.org


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>