spi: dw: Set xfer effective_speed_hz

Seeing DW APB SSI controller doesn't support setting the exactly
requested SPI bus frequency, but only a rounded frequency determined
by means of the odd-numbered half-worded reference clock divider,
it would be good to tune the SPI core up and initialize the current
transfer effective_speed_hz. By doing so the core will be able to
execute the xfer-related delays with better accuracy.
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org
Link: https://lore.kernel.org/r/20200529131205.31838-2-Sergey.Semin@baikalelectronics.ruSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.c

@@ -352,6 +352,7 @@ static int dw_spi_transfer_one(struct spi_controller *master,
 		spi_set_clk(dws, chip->clk_div);
 	}
 
+	transfer->effective_speed_hz = dws->max_freq / chip->clk_div;
 	dws->n_bytes = DIV_ROUND_UP(transfer->bits_per_word, BITS_PER_BYTE);
 
 	cr0 = dws->update_cr0(master, spi, transfer);