storvsc: fix auto-sense reporting

[avg]

Summary

I saw a situation where the driver set CAM_AUTOSNS_VALID on a failed ccb
even though SRB_STATUS_AUTOSENSE_VALID was not set in the status.
The actual sense data remained all zeros.
The problem seems to be that create_storvsc_request() always sets
hv_storvsc_request::sense_info_len, so checking for sense_info_len != 0
is not enough to determine if any auto-sense data is actually available.

[imp]

The cam part of this looks good. Don't know if that's the right bit to test, but it sure sounds like it

[whu]

Thanks for fixing this.