hpsa: fix handling of hpsa_volume_offline return value

Make return value an int instead of an unsigned char so that
we do not lose negative error return values.

Signed-off-by: Stephen M. Cameron <scameron@beardog.cce.hp.com>
Reviewed-by: Webb Scales <webb.scales@hp.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>