[SCSI] hptiop: fix header.context usage

header.context is a 64 bit field, but it's deliberately split into
context and context_hi32.  Thus cpu_to_le64 assignments are wrong on
this.  Replace them with the correct settings of both the low and high
words.

Cc: HighPoint Linux Team <linux@highpoint-tech.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>