cpufreq: conservative: Replace sscanf() with kstrtouint()

cpufreq: conservative: Replace sscanf() with kstrtouint()

Replace sscanf() with kstrtouint() in all sysfs store functions to improve
input validation and security. The kstrtouint() function provides better
error detection, overflow protection, and consistent error handling
compared to sscanf().

This maintains existing functionality while improving input validation
robustness and following kernel coding best practices for string parsing.

Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Link: https://patch.msgid.link/20250906115316.3010384-1-kaushlendra.kumar@intel.com
[ rjw: Dropped duplicate paragraph from the changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>