Staging: hv: Simplify blkvsc_init_rw()

Simplyfify blkvsc_init_rw() by using a single scsi command independent of
the start sector.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Hank Janssen <hjanssen@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>