cpufreq: unicore32: fix typo issue for 'clk'

Need use 'clk' instead of 'mclk', which is the original removed local
variable.

The related original commit:

"652ed95 cpufreq: introduce cpufreq_generic_get() routine"

The related error with allmodconfig for unicore32:

CC drivers/cpufreq/unicore2-cpufreq.o
drivers/cpufreq/unicore2-cpufreq.c: In function ‘ucv2_target’:
drivers/cpufreq/unicore2-cpufreq.c:48: error: ‘struct cpufreq_policy’ has no member named ‘mclk’
make[2]: *** [drivers/cpufreq/unicore2-cpufreq.o] Error 1
make[1]: *** [drivers/cpufreq] Error 2
make: *** [drivers] Error 2

Fixes: 652ed95d5fa6 (cpufreq: introduce cpufreq_generic_get() routine)
Signed-off-by: Chen Gang <[e-mail]>
Acked-by: Viresh Kumar <[e-mail]>
Cc: 3.14+ <[e-mail]> # 3.14+
Signed-off-by: Rafael J. Wysocki <[e-mail]>

drivers/cpufreq/unicore2-cpufreq.c

···
 	freqs.new = target_freq;
 
 	cpufreq_freq_transition_begin(policy, &freqs);
-	ret = clk_set_rate(policy->mclk, target_freq * 1000);
+	ret = clk_set_rate(policy->clk, target_freq * 1000);
 	cpufreq_freq_transition_end(policy, &freqs, ret);
 
 	return ret;