misc: xilinx_sdfec: Prevent a divide by zero in xsdfec_reg0_write()

The "psize" value comes from the user so we need to verify that it's
non-zero before we check if "n % psize" or it will crash.

Fixes: 20ec628e ("misc: xilinx_sdfec: Add ability to configure LDPC")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Michal Simek <michal.simek@xilinx.com>
Link: https://lore.kernel.org/r/20190821070953.GC26957@mwandaSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/misc/xilinx_sdfec.c

@@ -460,7 +460,7 @@ static int xsdfec_reg0_write(struct xsdfec_dev *xsdfec, u32 n, u32 k, u32 psize,
 {
 	u32 wdata;
 
-	if (n < XSDFEC_REG0_N_MIN || n > XSDFEC_REG0_N_MAX ||
+	if (n < XSDFEC_REG0_N_MIN || n > XSDFEC_REG0_N_MAX || psize == 0 ||
 	    (n > XSDFEC_REG0_N_MUL_P * psize) || n <= k || ((n % psize) != 0)) {
 		dev_dbg(xsdfec->dev, "N value is not in range");
 		return -EINVAL;