drm/msm/a6xx: fix frequency not always being restored on GMU resume

The patch reorganizing the set_freq function made it so the gmu resume
doesn't always set the frequency, because a6xx_gmu_set_freq() exits early
when the frequency hasn't been changed. Note this always happens when
resuming GMU after recovering from a hang.

Use a simple workaround to prevent this from happening.

Fixes: 1f60d114 ("drm: msm: a6xx: send opp instead of a frequency")
Signed-off-by: Jonathan Marek <jonathan@marek.ca>
Signed-off-by: Rob Clark <robdclark@chromium.org>