[SCSI] sg: increase sglist_len of the sg_scatter_hold structure

[SCSI] sg: increase sglist_len of the sg_scatter_hold structure

unsigned short is too small for sizeof(struct scatterlist) *
min(q->max_hw_segments, q->max_phys_segments).

This fixes memory leak with 4096 segments since 16 (likely sg size
with x86) * 4096 sets sglist_len to zero.

This might not happen without sg chaining support.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Acked-by: Douglas Gilbert <dougg@torque.net>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>