scsi: fas216: Mark expected switch fall-throughs

Mark switch cases where we are expecting to fall through.

Fix the following warnings (Building: rpc_defconfig arm):

drivers/scsi/arm/fas216.c: In function ‘fas216_disconnect_intr’:
drivers/scsi/arm/fas216.c:913:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if (fas216_get_last_msg(info, info->scsi.msgin_fifo) == ABORT) {
      ^
drivers/scsi/arm/fas216.c:919:2: note: here
  default:    /* huh?     */
  ^~~~~~~
drivers/scsi/arm/fas216.c: In function ‘fas216_kick’:
drivers/scsi/arm/fas216.c:1959:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   fas216_allocate_tag(info, SCpnt);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/arm/fas216.c:1960:2: note: here
  case TYPE_OTHER:
  ^~~~
drivers/scsi/arm/fas216.c: In function ‘fas216_busservice_intr’:
drivers/scsi/arm/fas216.c:1413:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   fas216_stoptransfer(info);
   ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/arm/fas216.c:1414:2: note: here
  case STATE(STAT_STATUS, PHASE_SELSTEPS):/* Sel w/ steps -> Status       */
  ^~~~
drivers/scsi/arm/fas216.c:1424:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   fas216_stoptransfer(info);
   ^~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/arm/fas216.c:1425:2: note: here
  case STATE(STAT_MESGIN, PHASE_COMMAND): /* Command -> Message In */
  ^~~~
drivers/scsi/arm/fas216.c: In function ‘fas216_funcdone_intr’:
drivers/scsi/arm/fas216.c:1573:6: warning: this statement may fall through [-Wimplicit-fallthrough=]
   if ((stat & STAT_BUSMASK) == STAT_MESGIN) {
      ^
drivers/scsi/arm/fas216.c:1579:2: note: here
  default:
  ^~~~~~~
drivers/scsi/arm/fas216.c: In function ‘fas216_handlesync’:
drivers/scsi/arm/fas216.c:605:20: warning: this statement may fall through [-Wimplicit-fallthrough=]
   info->scsi.phase = PHASE_MSGOUT_EXPECT;
   ~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~
drivers/scsi/arm/fas216.c:607:2: note: here
  case async:
  ^~~~

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>