tools/testing/cxl: Fix root port to host bridge assignment

Mocked root-ports are meant to be round-robin assigned to host-bridges.

Fixes: 67dcdd4d ("tools/testing/cxl: Introduce a mocked-up CXL port hierarchy")
Link: https://lore.kernel.org/r/164298431629.3018233.14004377108116384485.stgit@dwillia2-desk3.amr.corp.intel.comSigned-off-by: Dan Williams <dan.j.williams@intel.com>

tools/testing/cxl/test/cxl.c

@@ -558,7 +558,7 @@ static __init int cxl_test_init(void)
 
 	for (i = 0; i < ARRAY_SIZE(cxl_root_port); i++) {
 		struct platform_device *bridge =
-			cxl_host_bridge[i / NR_CXL_ROOT_PORTS];
+			cxl_host_bridge[i % ARRAY_SIZE(cxl_host_bridge)];
 		struct platform_device *pdev;
 
 		pdev = platform_device_alloc("cxl_root_port", i);