cpufreq: Remove needless bios_limit check in show_bios_limit()

Initially, bios_limit attribute will be created if driver->bios_limit
is set in cpufreq_add_dev_interface(). So remove the redundant check
for latter show operation.

Signed-off-by: Yue Hu <huyue2@yulong.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>