commit b0b48550 upstream.

XTFPGA SPI controller has native endian registers.
Fix register acessors so that they work in big-endian configurations.
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>