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

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: 20ec628e8007 ("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@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>