SCSI: storvsc: Initialize the sglist

commit 9d2696e6 upstream.

Properly initialize scatterlist before using it.

Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>