drm/amdgpu: fix get_max_engine_clock_in_mhz

[ Upstream commit a9efcc19161e20623c285fac967a32842972cebe ]

Use proper powerplay function. This fixes OpenCL initialization
problems.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Acked-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Oded Gabbay <oded.gabbay@gmail.com>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>