nios2: Fix ioremap

Commit 5ace77e0 ("nios2: remove __ioremap") removed the following code,
with the argument that cacheflag is always 0 and the expression would
therefore always be false.

	if (IS_MAPPABLE_UNCACHEABLE(phys_addr) &&
	    IS_MAPPABLE_UNCACHEABLE(last_addr) &&
	    !(cacheflag & _PAGE_CACHED))
		return (void __iomem *)(CONFIG_NIOS2_IO_REGION_BASE + phys_addr);

This did not take the "!" in the expression into account. Result is that
nios2 images no longer boot. Restoring the removed code fixes the problem.

Fixes: 5ace77e0 ("nios2: remove __ioremap")
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Ley Foon Tan <ley.foon.tan@intel.com>