sony-laptop: fix sony_nc_sysfs_store()

We made this an unsigned long and it causes a bug on 64 bit big endian
systems when we try to pass the value to sony_nc_int_call().

Also value has to be signed because validate() returns negative error
codes.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mattia Dongili <malattia@linux.it>
Signed-off-by: Matthew Garrett <mjg@redhat.com>