drm/msm/adreno: Remove a useless call to dev_pm_opp_get_freq()

Calling dev_pm_opp_find_freq_floor() returns the matched frequency
in 'freq'.  We don't need to call dev_pm_opp_get_freq() again
to get the frequency value.

Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>
Signed-off-by: Rob Clark <robdclark@gmail.com>