sony-laptop: fix uninitialised variable

drivers/misc/sony-laptop.c: In function 'sony_acpi_add':
drivers/misc/sony-laptop.c:456: warning: 'result' may be used uninitialized in this function

The compiler seems to actually be telling the truth this time.

Cc: Mattia Dongili <malattia@linux.it>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>