ANDROID: cpufreq: times: skip printing invalid frequencies

The header of /proc/uid_time_in_state should match the logic used for
the rest of the file by skipping invalid frequency table entries.

Test: Read /proc/uid_time_in_state and check for invalid frequencies
in header.
Signed-off-by: Connor O'Brien <connoro@google.com>

Change-Id: I96888e7b71f4928383ff7080c98c988d5fe1a95c