[SCSI] aha152x: Close narrow race in release

We were releasing the IRQ before removing the host, so commands could
still be coming in which would never be seen by the interrupt handler.
Just remove the host before releasing the IRQ to close this race.

Signed-off-by: Matthew Wilcox <matthew@wil.cx>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>