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

This patch fixes the following warning:

drivers/scsi/mpt3sas/mpt3sas_base.c: In function  _base_update_ioc_page1_inlinewith_perf_mode :
drivers/scsi/mpt3sas/mpt3sas_base.c:4510:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (ioc->high_iops_queues) {
      ^
drivers/scsi/mpt3sas/mpt3sas_base.c:4530:2: note: here
  case MPT_PERF_MODE_LATENCY:
  ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

This patch is part of the ongoing efforts to enable -Wimplicit-fallthrough.

Fixes: 30cb97023f38 ("scsi: mpt3sas: Introduce perf_mode module parameter")
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>