amd-xgbe: Handle return code from software reset function

Currently the function that performs a software reset of the hardware
provides a return code.  During driver probe check this return code and
exit with an error if the software reset fails.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>