mptfusion: fix msgContext in mptctl_hp_hostinfo

Hi,

without this patch the istwiRWRequest->MsgContext is always set to zero,
this patch saves the MsgContext in a msgcontext variable and then restores
the value.
Thanks to  David Jeffery who found the issue and did the analysis.

Signed-off-by: Tomas Henzl <thenzl@redhat.com>
Acked-by: Desai, Kashyap <Kashyap.Desai@lsi.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>