net/natsemi: Fix module parameter permissions

The third parameter of module_param is supposed to represent sysfs
file permissions. A value of "1" leads to the following:

$ ls -l /sys/module/natsemi/parameters/
total 0
---------x 1 root root 4096 Jul  8 09:46 dspcfg_workaround

I am changing it to "0" to align with the other module parameters in
this driver.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Tim Hockin <thockin@hockin.org>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: David S. Miller <davem@davemloft.net>