drm/amdgpu/psp13.0.4: replace BUG() with an error

There's no need to crash the kernel for this case.

Reviewed-by: Kent Russell <kent.russell@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/psp_v13_0_4.c

@@ -50,7 +50,9 @@ static int psp_v13_0_4_init_microcode(struct psp_context *psp)
 			return err;
 		break;
 	default:
-		BUG();
+		dev_warn(adev->dev, "Unsupported MP0 version 0x%08x\n",
+			 amdgpu_ip_version(adev, MP0_HWIP, 0));
+		return -EINVAL;
 	}
 
 	return 0;