platform/x86: asus-wmi: Replace sscanf() with kstrtoint()

The use of sscanf() is an overkill here. Moreover, there is no need to check
for count to be 0, since it's guaranteed by sysfs not to be.

Taking above into account, replace sscanf() with kstrtoint() calls.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>