The simple_strtol() function is not reliable in some situation, since
it does not check for the range overflow. Use kstrtol() instead.

While at it, modify the code to avoid evaluating _SEM unnecessarily
if uid_str is NULL or kstrtol() fails to convert that string to a
nonzero number.
Signed-off-by: Liu Shixin <liushixin2@huawei.com>
[ rjw: Check uid right after calling kstrtol() ]
[ rjw: Rewrite subject and changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>