Pick up changes in rev 1.8 of src/sys/dev/ic/mpt_netbsd.c from NetBSD.
Set the DMA SGL length correctly if the DMA request must be chained because
it is too large to fit in one SGL.

This should fix this driver for some Dell Precision systems.
RELENG_5 candidate.

PR: kern/66479
Submitted by: HITOSHI Osada <qfh02545@nifty.com>