spi: dw: Remove test for non-zero spi->max_speed_hz

Test for non-zero spi->max_speed_hz in dw_spi_setup() looks needless as
spi_setup() defaults to master->max_speed_hz in case it is not set. This
drivers sets the master->max_speed_hz based on max_freq data passed to it
via dw_spi_add_host() call. I suppose things have already fallen apart if
dw_spi_mmio_probe() or spi_pci_probe() ever passes zero max_freq.

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