net: phy: vitesse: Fix incorrect test for timeout

net: phy: vitesse: Fix incorrect test for timeout

In vsc8514_config there is a while loop for detecting a config failure
using a timeout counter with a post-decrement. In the case of a timeout
this will result in the loop exiting with timeout == -1 so use that as
the test below the loop to detect that the timeout occurred.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>
Reviewed-by: Quentin Schulz <quentin.schulz@cherry.de>