selftests/bpf: Fix btf leak on new btf alloc failure in btf_distill test

Fix btf leak on new btf alloc failure in btf_distill test.

Fixes: affdeb5 ("selftests/bpf: Extend distilled BTF tests to cover BTF relocation")
Signed-off-by: Pu Lehui <pulehui@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20250115100241.4171581-1-pulehui@huaweicloud.com

Author: Pu Lehui

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

@@ -385,7 +385,7 @@ static void test_distilled_base_missing_err(void)
 		"[2] INT 'int' size=8 bits_offset=0 nr_bits=64 encoding=SIGNED");
 	btf5 = btf__new_empty();
 	if (!ASSERT_OK_PTR(btf5, "empty_reloc_btf"))
-		return;
+		goto cleanup;
 	btf__add_int(btf5, "int", 4, BTF_INT_SIGNED);   /* [1] int */
 	VALIDATE_RAW_BTF(
 		btf5,
@@ -478,7 +478,7 @@ static void test_distilled_base_multi_err2(void)
 		"[1] INT 'int' size=4 bits_offset=0 nr_bits=32 encoding=SIGNED");
 	btf5 = btf__new_empty();
 	if (!ASSERT_OK_PTR(btf5, "empty_reloc_btf"))
-		return;
+		goto cleanup;
 	btf__add_int(btf5, "int", 4, BTF_INT_SIGNED);   /* [1] int */
 	btf__add_int(btf5, "int", 4, BTF_INT_SIGNED);   /* [2] int */
 	VALIDATE_RAW_BTF(