net: dsa: sja1105: propagate exact error code from sja1105_dynamic_config_poll_valid()

Currently, sja1105_dynamic_config_wait_complete() returns either 0 or
-ETIMEDOUT, because it just looks at the read_poll_timeout() return code.

There will be future changes which move some more checks to
sja1105_dynamic_config_poll_valid(). It is important that we propagate
their exact return code (-ENOENT, -EINVAL), because callers of
sja1105_dynamic_config_read() depend on them.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>