thermal: cpu_cooling: Remove CPU online validation

CPU cooling device validates if any of the CPU is online before getting
the cpufreq policy. There is no guarantee that the CPU will be online
till the policy is fetched using cpufreq_cpu_get().

cpufreq_cpu_get() acquires the necessary locks to prevent CPU
online/offline and then fetches the policy. If CPUs for which policy
is requested is offline, cpufreq_cpu_get will return NULL and cooling
device register will issue a probe defer. Since cpufreq_cpu_get is able
to handle the CPU being offline issue, remove the redundant check in CPU
cooling device register.

Change-Id: I302e5223a0db5fe942f24be6ec1102427a4ff133
Signed-off-by: Ram Chandrasekar <rkumbako@codeaurora.org>