Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings:

drivers/scsi/ibmvscsi/ibmvfc.c: In function 'ibmvfc_npiv_login_done':
drivers/scsi/ibmvscsi/ibmvfc.c:4022:3: warning: this statement may fall through [-Wimplicit-fallthrough=]
   ibmvfc_retry_host_init(vhost);
   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/ibmvscsi/ibmvfc.c:4023:2: note: here
  case IBMVFC_MAD_DRIVER_FAILED:
  ^~~~
drivers/scsi/ibmvscsi/ibmvfc.c: In function 'ibmvfc_bsg_request':
drivers/scsi/ibmvscsi/ibmvfc.c:1830:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
   port_id = (bsg_request->rqst_data.h_els.port_id[0] << 16) |
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    (bsg_request->rqst_data.h_els.port_id[1] << 8) |
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    bsg_request->rqst_data.h_els.port_id[2];
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/ibmvscsi/ibmvfc.c:1833:2: note: here
  case FC_BSG_RPT_ELS:
  ^~~~
drivers/scsi/ibmvscsi/ibmvfc.c:1838:11: warning: this statement may fall through [-Wimplicit-fallthrough=]
   port_id = (bsg_request->rqst_data.h_ct.port_id[0] << 16) |
   ~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    (bsg_request->rqst_data.h_ct.port_id[1] << 8) |
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    bsg_request->rqst_data.h_ct.port_id[2];
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/ibmvscsi/ibmvfc.c:1841:2: note: here
  case FC_BSG_RPT_CT:
  ^~~~
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Tyrel Datwyler <tyreld@linux.ibm.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>