sg: prevent integer overflow when converting from sectors to bytes

sg: prevent integer overflow when converting from sectors to bytes

commit 46f69e6a6bbbf3858617c8729e31895846c15a79 upstream.

This prevents integer overflow when converting the request queue's
max_sectors from sectors to bytes.  However, this is a preparation for
extending the data type of max_sectors in struct Scsi_Host and
scsi_host_template.  So, it is impossible to happen this integer
overflow for now, because SCSI low-level drivers can not specify
max_sectors greater than 0xffff due to the data type limitation.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>