tick: don't update idle time if cpu offline

An offline cpu still has ts->idle_active == 1, that cause
off time is counted as idle time, and hence cause cpu load
calculated wrongly.

Check the cpu online status before updating the idle time to
fix it.

Change-Id: I00deb4cbcaec18f7625ee774bf4c3e643330dd5f
Signed-off-by: Lianwei Wang <a22439@motorola.com>
Reviewed-on: http://gerrit.mot.com/695764


SLTApproved: Slta Waiver <sltawvr@motorola.com>
Tested-by: Jira Key <jirakey@motorola.com>
Reviewed-by: Christopher Fries <cfries@motorola.com>
Reviewed-by: Igor Kovalenko <igork@motorola.com>
Submit-Approved: Jira Key <jirakey@motorola.com>
[picked from http://goo.gl/lLF51X

]
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>

Used commits:
 https://github.com/mythos234/SimplKernel-LL-G925F/commit/1c9f26ace4386201f4ea493b94b9edb064c6c090
 https://github.com/alexax66/kernel_samsung_a3xelte/commit/ba403c974ef439899cc76528a9df1e876dd58293