[SCSI] Add scsi_add_host() failure handling for nsp32

Add scsi_add_host() failure handling for nsp32
and silence warning.
  drivers/scsi/nsp32.c:2888: warning: ignoring return value of 'Scsi_add_host', declared with attribute warn_unused_result

Signed-off-by: Jesper Juhl <jesper.juhl@gmail.com>
Signed-off-by: GOTO Masanori <gotom@sanori.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: James Bottomley <James.Bottomley@SteelEye.com>