cpufreq: sparc: call cpufreq_frequency_table_get_attr()

This exposes frequency table of driver to cpufreq core and is required for core
to guess what the index for a target frequency is, when it calls
cpufreq_frequency_table_target(). And so this driver needs to expose it.

Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>