cpufreq: ti-cpufreq: Mark expected switch fall-through

Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: arm):

drivers/cpufreq/ti-cpufreq.c: In function ‘dra7_efuse_xlate’:
drivers/cpufreq/ti-cpufreq.c:79:20: warning: this statement may fall through [-Wimplicit-fallthrough=]
   calculated_efuse |= DRA7_EFUSE_HIGH_MPU_OPP;
drivers/cpufreq/ti-cpufreq.c:80:2: note: here
  case DRA7_EFUSE_HAS_OD_MPU_OPP:
  ^~~~

Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>