usb: fix storage regression

Fix the contition to figure whenever we need to wait for more data or
not.  Simply check the mode, if we are not in DATAIN state any more we
are done already and don't need to go ASYNC.

Fixes: 7ad3d51e ("usb: add short-packet handling to usb-storage driver")
Reported-by: NSai Pavan Boddu <saipava@xilinx.com>
Tested-by: NPaul Zimmerman <pauldzim@gmail.com>
Signed-off-by: NGerd Hoffmann <kraxel@redhat.com>
Message-id: 20200713062712.1476-1-kraxel@redhat.com

hw/usb/dev-storage.c

@@ -546,8 +546,7 @@ static void usb_msd_handle_data(USBDevice *dev, USBPacket *p)
                     }
                 }
             }
-            if (p->actual_length < p->iov.size && (p->short_not_ok ||
-                    s->scsi_len >= p->ep->max_packet_size)) {
+            if (p->actual_length < p->iov.size && s->mode == USB_MSDM_DATAIN) {
                 DPRINTF("Deferring packet %p [wait data-in]\n", p);
                 s->packet = p;
                 p->status = USB_RET_ASYNC;