hyperv/storvsc: Deliver CAM_SEL_TIMEOUT upon SRB status error.

SRB status is set to 0x20 by the hypervisor, if the specified LUN is
unaccessible, and even worse the INQUIRY response will not be set by
the hypervisor at all under this situation. Additionally, SRB status
is 0x20 too, for TUR on an unaccessible LUN.

Deliver CAM_SEL_TIMEOUT to CAM upon SRB status errors as suggested by
Scott Long, other values seems improper.

This commit fixes the Hyper-V disk hotplug support.

Submitted by: Hongjiang Zhang <honzhan microsoft com>
MFC after: 3 days
Sponsored by: Microsoft
Differential Revision: https://reviews.freebsd.org/D7521