cpufreq: interactive: Use default min_sample_time if SDF is zero

Use min_sample_time to step down from max frequencies if
sampling_down_factor is set to zero.

Change-Id: I2e89bef6220557cb95efd20d658e0c05753b4c3c
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>