[SCSI] zalon: fix oops on attach failure

I recently discovered on my zalon that if the attachment fails because
of a bus misconfiguration (I scrapped my HVD array, so the card is now
unterminated) then the system oopses.  The reason is that if
ncr_attach() returns NULL (signalling failure) that NULL is passed by
the goto failed straight into ncr_detach() which oopses.

The fix is just to return -ENODEV in this case.

Cc: Stable Tree <stable@kernel.org>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>