crypto: nx - nx842_OF_upd_status should return ENODEV if device is not 'okay'

The current documention mentions explicitly that EINVAL should be
returned if the device is not available, but nx842_OF_upd_status()
always returns 0. However, nx842_probe() specifically checks for
non-ENODEV returns from nx842_of_upd() (which in turn calls
nx842_OF_upd_status()) and emits an extra error in that case. It seems
like the proper return code of a disabled device is ENODEV.

Signed-off-by: Nishanth Aravamudan <nacc@linux.vnet.ibm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>