tools/cpupower: Fix incorrect size in cpuidle_state_disable()

tools/cpupower: Fix incorrect size in cpuidle_state_disable()

Fix incorrect size parameter passed to cpuidle_state_write_file() in
cpuidle_state_disable().

The function was incorrectly using sizeof(disable) which returns the
size of the unsigned int variable (4 bytes) instead of the actual
length of the string stored in the 'value' buffer.

Since 'value' is populated with snprintf() to contain the string
representation of the disable value, we should use the length
returned by snprintf() to get the correct string length for
writing to the sysfs file.

This ensures the correct number of bytes is written to the cpuidle
state disable file in sysfs.

Link: https://lore.kernel.org/r/20250917050820.1785377-1-kaushlendra.kumar@intel.com
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>