fec_main.c edit to fix MDIO read/write timeouts, bringing the network adapter down.

Without this patch, essentially reverting Uwe Kleine-König's patch that fixes problems for -rt patched Linux,
there is a race condition (which I'm not sure how to track down) which has the network up when an imx28-cfa100xx
based device boots, then experiences an MDIO rx timeout, and drops the network until it's ifdown/ifup'd.