libbpf: Fix memory leak in parse_usdt_arg()

libbpf: Fix memory leak in parse_usdt_arg()

[ Upstream commit 0dc9254e03704c75f2ebc9cbef2ce4de83fba603 ]

In the arm64 version of parse_usdt_arg(), when sscanf returns 2, reg_name
is allocated but not freed. Fix it.

Fixes: 0f8619929c57 ("libbpf: Usdt aarch64 arg parsing support")
Signed-off-by: Xu Kuohai <xukuohai@huawei.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Martin KaFai Lau <martin.lau@kernel.org>
Link: https://lore.kernel.org/bpf/20221011120108.782373-3-xukuohai@huaweicloud.com
Signed-off-by: Sasha Levin <sashal@kernel.org>