[SCSI] hpsa: avoid leaking stack contents to userland

memset arg64 to zero in the passthrough ioctls to avoid leaking contents
of kernel stack memory to userland via uninitialized padding fields
inserted by the compiler for alignment reasons.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>