drm/amdgpu/sriov: workaround on rev_id for Navi12 under sriov

guest vm gets 0xffffffff when reading RCC_DEV0_EPF0_STRAP0,
as a consequence, the rev_id and external_rev_id are wrong.

workaround it by hardcoding the rev_id to 0, which is the default value.

v2. add comment in the code
Signed-off-by: Tiecheng Zhou <Tiecheng.Zhou@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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

@@ -726,6 +726,12 @@ static int nv_common_early_init(void *handle)
 			AMD_PG_SUPPORT_VCN_DPG |
 			AMD_PG_SUPPORT_JPEG |
 			AMD_PG_SUPPORT_ATHUB;
+		/* guest vm gets 0xffffffff when reading RCC_DEV0_EPF0_STRAP0,
+		 * as a consequence, the rev_id and external_rev_id are wrong.
+		 * workaround it by hardcoding rev_id to 0 (default value).
+		 */
+		if (amdgpu_sriov_vf(adev))
+			adev->rev_id = 0;
 		adev->external_rev_id = adev->rev_id + 0xa;
 		break;
 	default: