[SCSI] mpt2sas: Call init_completion on a per request basis.

Now driver call init_completion on a per request basis.  At some
point the wait_for_completion_timeout is not waiting for the timeout,
instead returning immediately, thus going into diag reset.  This fix will
address all request using the wait_for_completion_timeout API. The previous
implimentation was only calling init_completion at driver
load time.

Signed-off-by: Kashyap Desai <kashyap.desai@lsi.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>