kobject: WARN as tip when call kobject_get() to a kobject not initialized

call kobject_get() to kojbect that is not initalized or released will only
leave following like call trace to us:

-----------[ cut here ]------------
[   54.545816] WARNING: CPU: 0 PID: 213 at include/linux/kref.h:47
kobject_get+0x41/0x50()
[   54.642595] Modules linked in: i2c_i801(+) mfd_core shpchp(+)
acpi_cpufreq(+) edac_core ioatdma(+) xfs libcrc32c ast syscopyarea ixgbe
sysfillrect sysimgblt sr_mod sd_mod drm_kms_helper igb mdio cdrom e1000e ahci
dca ttm libahci uas drm i2c_algo_bit ptp megaraid_sas libata usb_storage
i2c_core pps_core dm_mirror dm_region_hash dm_log dm_mod
[   55.007264] CPU: 0 PID: 213 Comm: kworker/0:2 Not tainted
3.18.5
[   55.099970] Hardware name: Oracle Corporation SUN FIRE X4170 M2 SERVER
   /ASSY,MOTHERBOARD,X4170, BIOS 08120104 05/08/2012
[   55.239736] Workqueue: kacpi_notify acpi_os_execute_deferred
[   55.308598]  0000000000000000 00000000bd730b61 ffff88046742baf8
ffffffff816b7edb
[   55.398305]  0000000000000000 0000000000000000 ffff88046742bb38
ffffffff81078ae1
[   55.488040]  ffff88046742bbd8 ffff8806706b3000 0000000000000292
0000000000000000
[   55.577776] Call Trace:
[   55.608228]  [<ffffffff816b7edb>] dump_stack+0x46/0x58
[   55.670895]  [<ffffffff81078ae1>] warn_slowpath_common+0x81/0xa0
[   55.743952]  [<ffffffff81078bfa>] warn_slowpath_null+0x1a/0x20
[   55.814929]  [<ffffffff8130d0d1>] kobject_get+0x41/0x50
[   55.878654]  [<ffffffff8153e955>] cpufreq_cpu_get+0x75/0xc0
[   55.946528]  [<ffffffff8153f37e>] cpufreq_update_policy+0x2e/0x1f0

The above issue was casued by a race condition, if there is a WARN in
kobject_get() of the kobject is not initialized, that would save us much
time to debug it.

Signed-off-by: Ethan Zhao <ethan.zhao@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>