net/fec_mpc52xx: Fix kernel panic on FEC error

The MDIO bus cannot be accessed at interrupt context, but on an FEC
error, the fec_mpc52xx driver reset function also tries to reset the
PHY.  Since the error is detected at IRQ context, and the PHY functions
try to sleep, the kernel ends up panicking.

Resetting the PHY on an FEC error isn't even necessary.  This patch
solves the problem by removing the PHY reset entirely.

Signed-off-by: John Bonesio <bones@secretlab.ca>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>