selftests/bpf: Add a missing newline to the "bad arch spec" message

Fix error messages like this one:

parse_test_spec:FAIL:569 bad arch spec: 's390x'process_subtest:FAIL:1153 Can't parse test spec for program 'may_goto_simple'

Signed-off-by: Ilya Leoshkevich <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Alexei Starovoitov <[e-mail]>

tools/testing/selftests/bpf/test_loader.c

···
 			} else if (strcmp(val, "RISCV64") == 0) {
 				arch = ARCH_RISCV64;
 			} else {
-				PRINT_FAIL("bad arch spec: '%s'", val);
+				PRINT_FAIL("bad arch spec: '%s'\n", val);
 				err = -EINVAL;
 				goto cleanup;
 			}