msm: kgsl: Only call dev_pm_opp_put on a valid OPP

If dev_pm_opp_find_freq_floor or dev_pm_opp_find_freq_ceil
cannot find a frequency that meets the criteria, they
will return an error instead of a valid pointer. Calling
dev_pm_opp_put on this error will lead to a page fault.
Skip calling dev_pm_opp_put in the error case.

CRs-Fixed: 2318681
Change-Id: I89a0a4a9bf67311ae5cf0f03d394876fa068ae85
Signed-off-by: Kyle Piefer <kpiefer@codeaurora.org>