spi: spi-bfin5xx: Calculate transfer speed unconditionally

SPI core validates the transfer speed and defaults to spi->max_speed_hz in
case the transfer speed is not set so code here won't use the
chip->baud value (which is derived from spi->max_speed_hz).

Please note driver uses chip->baud at the beginning of message transmission
by calling the bfin_spi_restore_state() but then programs per transfer
speed in bfin_spi_pump_transfers(). I'm not familiar with the HW so I don't
know would it be possible to remove chip->baud completely by either using
constant value in bfin_spi_restore_state() or by removing the baud register
write there.

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