spi: atmel: Remove needless bits_per_word and speed_hz tests

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 makes possible to remove two if
statements and remove one code block that is never executed.

Signed-off-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>