selftests/bpf: Close obj in error path in xdp_adjust_tail

If bpf_object__load() fails in test_xdp_adjust_frags_tail_grow(), "obj"
opened before this should be closed. So use "goto out" to close it instead
of using "return" here.

Fixes: 1102210 ("bpf: selftests: update xdp_adjust_tail selftest to include xdp frags")
Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
Link: https://lore.kernel.org/r/f282a1ed2d0e3fb38cceefec8e81cabb69cab260.1720615848.git.tanggeliang@kylinos.cn
Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>

tools/testing/selftests/bpf/prog_tests/xdp_adjust_tail.c

@@ -222,7 +222,7 @@ static void test_xdp_adjust_frags_tail_grow(void)
 
 	prog = bpf_object__next_program(obj, NULL);
 	if (bpf_object__load(obj))
-		return;
+		goto out;
 
 	prog_fd = bpf_program__fd(prog);