spi: spi-ep93xx: remove bits_per_word() helper

Check t->bits_per_word directly and remove the inline helper function.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Mika Westerberg <mika.westerberg@iki.fi>
Signed-off-by: Mark Brown <broonie@linaro.org>