spi: atmel-quadspi: drop wrappers for iomem accesses

The wrappers hid that the accesses are relaxed. Drop them.

Suggested-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Tudor Ambarus <tudor.ambarus@microchip.com>
Reviewed-by: Boris Brezillon <bbrezillon@kernel.org>
Signed-off-by: Mark Brown <broonie@kernel.org>