spi: omap-100k: Rely on validations done by spi core

SPI core validates both bits_per_word and speed_hz transfer parameters and
defaults to spi->bits_per_word and spi->max_speed_hz in case these per
transfer parameters are not set.

This allows to remove a few if statements around per transfer bits_per_word
and speed_hz tests as they evaluate always to true.

Also defaulting word_len to 8 is needless since spi_setup() has already
made sure spi->bits_per_word is 8 in case it is not set.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>