net: phy: at803x: refactor qca808x cable test get status function

Refactor qca808x cable test get status function to remove code
duplication and clean things up.

The same logic is applied to each pair hence it can be generalized and
moved to a common function.

Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>