[PATCH v2] spi: spi-cadence-quadspi: Fix division by zero warning

[Yoshitaka Ikeda <ikeda@xxxxxxxxxxxx>]

Fix below division by zero warning:
- Added an if statement because buswidth can be zero, resulting in division by zero.
- The modified code was based on another driver (atmel-quadspi).

[    0.795337] Division by zero in kernel.
   :
[    0.834051] [<807fd40c>] (__div0) from [<804e1acc>] (Ldiv0+0x8/0x10)
[    0.839097] [<805f0710>] (cqspi_exec_mem_op) from [<805edb4c>] (spi_mem_exec_op+0x3b0/0x3f8)

Signed-off-by: Yoshitaka Ikeda <ikeda@xxxxxxxxxxxx>
---
v2:
- Fix commit message.
---
   drivers/spi/spi-cadence-quadspi.c | 10 ++++++----
   1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-cadence-quadspi.c b/drivers/spi/spi-cadence-quadspi.c
index 7a00346ff9b9..13d1f0ce618e 100644
--- a/drivers/spi/spi-cadence-quadspi.c
+++ b/drivers/spi/spi-cadence-quadspi.c
@@ -307,11 +307,13 @@ static unsigned int cqspi_calc_rdreg(struct cqspi_flash_pdata *f_pdata)
   
   static unsigned int cqspi_calc_dummy(const struct spi_mem_op *op, bool dtr)
   {
-	unsigned int dummy_clk;
+	unsigned int dummy_clk = 0;
   
-	dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
-	if (dtr)
-		dummy_clk /= 2;
+	if (op->dummy.buswidth && op->dummy.nbytes) {
+		dummy_clk = op->dummy.nbytes * (8 / op->dummy.buswidth);
+		if (dtr)
+			dummy_clk /= 2;
+	}
   
   	return dummy_clk;
   }
-- 
2.32.0