spi: xcomm: Use devm_spi_register_master()

Use devm_spi_register_master() to make cleanup paths simpler,
and remove unnecessary remove().

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Mark Brown <broonie@linaro.org>