ata: pata_octeon_cf: fix error return code in octeon_cf_probe()

The variable 'rv' is set to 0 after calling of_property_read_reg(), so
it cannot be used as an error code. Change to using correct error codes
in the error path.

Fixes: d0b24616

 ("ata: Use of_property_read_reg() to parse "reg"")
Signed-off-by: Yang Yingliang <yangyingliang@huawei.com>
Reviewed-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>