kms_pipe_crc_basic: Use igt_display_get_n_pipes() instead of hardcoding 3

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

tests/kms_pipe_crc_basic.c

@@ -169,7 +169,7 @@ igt_main
 	igt_subtest("bad-nb-words-3")
 		test_bad_command(&data, "pipe A none option");
 
-	for (int i = 0; i < 3; i++) {
+	for (int i = 0; i < igt_display_get_n_pipes(&data.display); i++) {
 		igt_subtest_f("read-crc-pipe-%c", 'A'+i)
 			test_read_crc(&data, i, 0);