cpufreq: qcom-cpufreq: Check return of cpufreq_frequency_get_table

cpufreq_frequency_get_table could return NULL. Do error check on the
return value instead of continue with a potentially NULL pointer.

Change-Id: I0cb8a3a8ae3499e738683e5f45271aeadee488f6
Signed-off-by: Junjie Wu <junjiew@codeaurora.org>