pvscsi: Explicitly mask out CTS_SAS_VALID_SPEED bit

This driver prefers connection speed over sas port speed. On stable/13
branch the stack-allocated CCB is not cleared thus the cam layer may
report weird speed on boot.

```
da0: <VMware Virtual disk 2.0> Fixed Direct Access SPC-4 SCSI device
da0: 4294967.295MB/s transfers
```

-current and stable/14 have the change [1] which clears stack-allocated
CCB thus are not affected, but I want -current and stable/14 to have this
fix in to reduce drift between branches.

1. ec5325d cam: make sure to clear even more CCBs allocated on the stack

Reviewed by:	imp
MFC after:	3 days
Differential Revision:	https://reviews.freebsd.org/D48438

sys/dev/vmware/pvscsi/pvscsi.c

@@ -1444,6 +1444,10 @@ pvscsi_action(struct cam_sim *sim, union ccb *ccb)
 		cts->proto_specific.scsi.flags = CTS_SCSI_FLAGS_TAG_ENB;
 		cts->proto_specific.scsi.valid = CTS_SCSI_VALID_TQ;
 
+		/* Prefer connection speed over sas port speed */
+		cts->xport_specific.sas.valid &= ~CTS_SAS_VALID_SPEED;
+		cts->xport_specific.sas.bitrate = 0;
+
 		ccb_h->status = CAM_REQ_CMP;
 		xpt_done(ccb);
 	} break;