stmmac: intel: Eliminate useless conditions and variables

There are useless conditions like

	func()
	{
		...
		int ret;
		...
		ret = foo();
		if (ret)
			return ret;

		return 0;
	}

which may be replaced with direct return statement, what we have done here.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>