spi: Fixed division by zero warning

The reason for dividing by zero is because the dummy bus width is zero,
but if the dummy n bytes is zero, it indicates that there is no data transfer,
so there is no need for calculation.

Fixes: 7512eaf54190 ("spi: cadence-quadspi: Fix dummy cycle calculation when buswidth > 1")
Signed-off-by: Yoshitaka Ikeda <[e-mail]>
Acked-by: Pratyush Yadav <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/atmel-quadspi.c

···
 		return mode;
 	ifr |= atmel_qspi_modes[mode].config;
 
-	if (op->dummy.buswidth && op->dummy.nbytes)
+	if (op->dummy.nbytes)
 		dummy_cycles = op->dummy.nbytes * 8 / op->dummy.buswidth;
 
 	/*

drivers/spi/spi-bcm-qspi.c

···
 	if (addrlen == BSPI_ADDRLEN_4BYTES)
 		bpp = BSPI_BPP_ADDR_SELECT_MASK;
 
-	bpp |= (op->dummy.nbytes * 8) / op->dummy.buswidth;
+	if (op->dummy.nbytes)
+		bpp |= (op->dummy.nbytes * 8) / op->dummy.buswidth;
 
 	switch (width) {
 	case SPI_NBITS_SINGLE:

drivers/spi/spi-mtk-nor.c

···
 {
 	int dummy = 0;
 
-	if (op->dummy.buswidth)
+	if (op->dummy.nbytes)
 		dummy = op->dummy.nbytes * BITS_PER_BYTE / op->dummy.buswidth;
 
 	if ((op->data.buswidth == 2) || (op->data.buswidth == 4)) {

drivers/spi/spi-stm32-qspi.c

···
 		ccr |= FIELD_PREP(CCR_ADSIZE_MASK, op->addr.nbytes - 1);
 	}
 
-	if (op->dummy.buswidth && op->dummy.nbytes)
+	if (op->dummy.nbytes)
 		ccr |= FIELD_PREP(CCR_DCYC_MASK,
 				  op->dummy.nbytes * 8 / op->dummy.buswidth);