drm/amdgpu: Fix use of interruptible waiting

There is no good mechanism to handle the corresponding error.
When signal interrupt happens, unpin is not called.
As a result, inside AMDGPU, the statistic of pin size will be wrong.

Signed-off-by: Alex Xie <AlexBin.Xie@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>