[SCSI] hpsa: take the adapter lock in hpsa_wait_for_mode_change_ack

Need to take the lock while accessing the register to check to
see if config table changes have taken effect.

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