cpufreq: ia64: Remove unused header files

seq_file.h does not need to be included, so remove it. Moreover deleted
a line of meaningless return and some useless blank lines. In a function
whose return type is void, returning on the last line is not required.

Signed-off-by: Yangtao Li <tiny.windzz@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>