s390x/pci: add some fallthrough annotations

According to the comment, the bits are supposed to accumulate.

Reported-by: Stefan Weil <sw@weilnetz.de>
Fixes: 5d1abf2 ("s390x/pci: enforce zPCI state checking")
Acked-by: Collin Walling <walling@linux.ibm.com>
Signed-off-by: Cornelia Huck <cohuck@redhat.com>

hw/s390x/s390-pci-inst.c

@@ -1209,8 +1209,10 @@ int stpcifc_service_call(S390CPU *cpu, uint8_t r1, uint64_t fiba, uint8_t ar,
      * FH Enabled bit is set to one in states of ENABLED, BLOCKED or ERROR. */
     case ZPCI_FS_ERROR:
         fib.fc |= 0x20;
+        /* fallthrough */
     case ZPCI_FS_BLOCKED:
         fib.fc |= 0x40;
+        /* fallthrough */
     case ZPCI_FS_ENABLED:
         fib.fc |= 0x80;
         if (pbdev->iommu->enabled) {