devfreq: don't set last_scale for same freq

devfreq: don't set last_scale for same freq

In nvhost_pod_estimate_freq(), we have *freq = 0
in case we decide to keep same frequency
In that case we set *freq as current frequency and
then set last_scale timestamp

This can result in keeping same frequency for
long duration due to less delta from last_scale

To fix this, return immediately in case *freq
is zero and do not set last_scale timestamp

Bug 200255163

Change-Id: Ie13bf54e2415c4016a101b9ea12a9abda83240fd
Signed-off-by: Deepak Nibade <dnibade@nvidia.com>
Reviewed-on: http://git-master/r/1265185
Reviewed-by: Automatic_Commit_Validation_User
GVS: Gerrit_Virtual_Submit
Reviewed-by: Wen Yi <wyi@nvidia.com>
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>