cpufreq: brcmstb-avs-cpufreq: fix up "add check for cpufreq_cpu_get's return value"

In commit e72160cb

 ("cpufreq: brcmstb-avs-cpufreq: add check for
cpufreq_cpu_get's return value"), build warnings occur because a
variable is created after some logic, resulting in:

drivers/cpufreq/brcmstb-avs-cpufreq.c: In function 'brcm_avs_cpufreq_get':
drivers/cpufreq/brcmstb-avs-cpufreq.c:486:9: error: ISO C90 forbids mixed
declarations and code [-Werror=declaration-after-statement]
  486 |         struct private_data *priv = policy->driver_data;
      |         ^~~~~~
cc1: all warnings being treated as errors
make[2]: *** [scripts/Makefile.build:289:
drivers/cpufreq/brcmstb-avs-cpufreq.o] Error 1
make[1]: *** [scripts/Makefile.build:552: drivers/cpufreq] Error 2
make[1]: *** Waiting for unfinished jobs....
make: *** [Makefile:1907: drivers] Error 2

Fix this up.

Link: https://lore.kernel.org/r/e114d9e5-26af-42be-9baa-72c3a6ec8fe5@oracle.com
Link: https://lore.kernel.org/stable/20240327015023.GC7502@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net/T/#m15bff0fe96986ef780e848b4fff362bf8ea03f08
Reported-by: Harshit Mogalapalli <harshit.m.mogalapalli@oracle.com>
Reported-by: Linux Kernel Functional Testing <lkft@linaro.org>
Fixes: e72160cb

 ("cpufreq: brcmstb-avs-cpufreq: add check for cpufreq_cpu_get's return value")
Cc: Anastasia Belova <abelova@astralinux.ru>
Cc: Viresh Kumar <viresh.kumar@linaro.org>
Cc: Sasha Levin <sashal@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>