msm: kgsl: Remove unnecssary call to dev_pm_opp_get_freq()

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

Change-Id: I725653b60f28073865e9a4734d81ad1d64530735
Signed-off-by: Deepak Kumar <dkumar@codeaurora.org>