spi: cadence-quadspi: Fix dummy cycle calculation when buswidth > 1

SPI MEM deals with dummy bytes but the controller deals with dummy
cycles. Multiplying bytes by 8 is correct if the dummy phase uses 1S
mode since 1 byte will be sent in 8 cycles. But if the dummy phase uses
4S mode then 1 byte will be sent in 2 cycles.

To correctly translate dummy bytes to dummy cycles, the dummy buswidth
also needs to be taken into account. Divide 8 by the buswidth to get the
correct multiplier for getting the number of cycles.
Signed-off-by: Pratyush Yadav <p.yadav@ti.com>
Link: https://lore.kernel.org/r/20201222184425.7028-5-p.yadav@ti.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-cadence-quadspi.c

@@ -294,7 +294,7 @@ static unsigned int cqspi_calc_dummy(const struct spi_mem_op *op)
 {
 	unsigned int dummy_clk;
 
-	dummy_clk = op->dummy.nbytes * 8;
+	dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
 
 	return dummy_clk;
 }