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

This patch fixes the following warnings:

drivers/message/fusion/mptscsih.c: In function  mptscsih_io_done :
drivers/message/fusion/mptscsih.c:741:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if ( ioc->bus_type == SAS ) {
       ^
drivers/message/fusion/mptscsih.c:790:3: note: here
   case MPI_IOCSTATUS_SCSI_TASK_TERMINATED: /* 0x0048 */
   ^~~~
drivers/message/fusion/mptscsih.c:884:4: warning: this statement may fall through [-Wimplicit-fallthrough=]
    scsi_set_resid(sc, 0);
    ^~~~~~~~~~~~~~~~~~~~~
drivers/message/fusion/mptscsih.c:885:3: note: here
   case MPI_IOCSTATUS_SCSI_RECOVERED_ERROR: /* 0x0040 */
   ^~~~

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

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>