tools/cpupower: Use strcspn() to strip trailing newline

Replace manual newline removal with strcspn() which is safer and
cleaner. This avoids potential out-of-bounds access on empty strings
and handles the case where no newline exists.

Link: https://lore.kernel.org/r/20251127044536.715722-1-kaushlendra.kumar@intel.com
Signed-off-by: Kaushlendra Kumar <kaushlendra.kumar@intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: kaushlen

tools/power/cpupower/lib/cpuidle.c

@@ -193,8 +193,7 @@ static char *cpuidle_state_get_one_string(unsigned int cpu,
 	if (result == NULL)
 		return NULL;
 
-	if (result[strlen(result) - 1] == '\n')
-		result[strlen(result) - 1] = '\0';
+	result[strcspn(result, "\n")] = '\0';
 
 	return result;
 }
@@ -366,8 +365,7 @@ static char *sysfs_cpuidle_get_one_string(enum cpuidle_string which)
 	if (result == NULL)
 		return NULL;
 
-	if (result[strlen(result) - 1] == '\n')
-		result[strlen(result) - 1] = '\0';
+	result[strcspn(result, "\n")] = '\0';
 
 	return result;
 }