drm/amdgpu: correct in_suspend setting for navi series

in_suspend flag should be set in amdgpu_device_suspend/resume in pairs,
instead of gfx10 ip suspend/resume function.

Signed-off-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>