spi: pxa2xx: pxa2xx_spi_transfer_one() can be static

Fixes: d5898e19 ("spi: pxa2xx: Use core message processing loop")
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Reviewed-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>