drm/amdgpu: Fix validating flush_gpu_tlb_pasid()

drm/amdgpu: Fix validating flush_gpu_tlb_pasid()

When a function holds a lock and we return without unlocking it,
it deadlocks the kernel. We should always unlock before returning.

This commit fixes suspend/resume on SI.
Tested on two Tahiti GPUs: FirePro W9000 and R9 280X.

Fixes: f4db9913e4d3 ("drm/amdgpu: validate the flush_gpu_tlb_pasid()")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202601190121.z9C0uml5-lkp@intel.com/
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Prike Liang <Prike.Liang@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>