cpufreq: docs: Update core.rst

As the definition of struct cpufreq_freqs has changed, update core.rst
with the new first member of struct cpufreq_freqs.

Signed-off-by: Tang Yizhou <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Signed-off-by: Rafael J. Wysocki <[e-mail]>

Documentation/cpu-freq/core.rst

···
 The third argument is a struct cpufreq_freqs with the following
 values:
 
-=====	===========================
-cpu	number of the affected CPU
+======	======================================
+policy	a pointer to the struct cpufreq_policy
 old	old frequency
 new	new frequency
 flags	flags of the cpufreq driver
-=====	===========================
+======	======================================
 
 3. CPUFreq Table Generation with Operating Performance Point (OPP)
 ==================================================================