net: ethernet: aquantia: Removed busy_count field.

 busy_count field and is_busy flag is not needed at all.

Signed-off-by: Pavel Belous <pavel.belous@aquantia.com>
Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>