hpsa: shorten the wait for the CISS doorbell mode change ack

Shorten the wait for the CISS configuration table doorbell mode
change acknowledgment from 300-600 s to 20 s, which is the value
specified in the CISS specification that should be honored by
all controllers.

Wait using interruptible msleep() rather than uninterruptible
usleep_range(), which triggers rt_sched timeout errors if the
wait is long.

Reviewed-by: Scott Teel <scott.teel@pmcs.com>
Signed-off-by: Robert Elliott <elliott@hp.com>
Signed-off-by: Don Brace <don.brace@pmcs.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>