storvsc: fix auto-sense reporting

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.

Sponsored by: CyberSecure

(cherry picked from commit 8afecefd57c5ac95200f43227cd00f265154acee)