drm/amdgpu: set adev->num_vmhubs for gmc6,7,8

So that we properly handle them on older asics.

Fixes: 3ff985485b29 ("drm/amdgpu: Export function to flush TLB of specific vm hub")
Tested-by: Tom St Denis <[e-mail]>
Reviewed-by: Xiaojie Yuan <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

drivers/gpu/drm/amd/amdgpu/gmc_v6_0.c

···
 	int r;
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 
+	adev->num_vmhubs = 1;
+
 	if (adev->flags & AMD_IS_APU) {
 		adev->gmc.vram_type = AMDGPU_VRAM_TYPE_UNKNOWN;
 	} else {

drivers/gpu/drm/amd/amdgpu/gmc_v7_0.c

···
 	int r;
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 
+	adev->num_vmhubs = 1;
+
 	if (adev->flags & AMD_IS_APU) {
 		adev->gmc.vram_type = AMDGPU_VRAM_TYPE_UNKNOWN;
 	} else {

drivers/gpu/drm/amd/amdgpu/gmc_v8_0.c

···
 	int r;
 	struct amdgpu_device *adev = (struct amdgpu_device *)handle;
 
+	adev->num_vmhubs = 1;
+
 	if (adev->flags & AMD_IS_APU) {
 		adev->gmc.vram_type = AMDGPU_VRAM_TYPE_UNKNOWN;
 	} else {