amd-xgbe: Use disable_irq_nosync from within timer function

Since the Tx timer function runs in softirq context the driver needs
to call disable_irq_nosync instead of a disable_irq.

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