bpf: Remove unnecessary kfree(im_node) in lpm_trie_update_elem

bpf: Remove unnecessary kfree(im_node) in lpm_trie_update_elem

[ Upstream commit 3d5611b4d7efbefb85a74fcdbc35c603847cc022 ]

There is no need to call kfree(im_node) when updating element fails,
because im_node must be NULL. Remove the unnecessary kfree() for
im_node.

Reviewed-by: Toke Høiland-Jørgensen <toke@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Hou Tao <houtao1@huawei.com>
Link: https://lore.kernel.org/r/20241206110622.1161752-3-houtao@huaweicloud.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Stable-dep-of: 532d6b36b2bf ("bpf: Handle in-place update for full LPM trie correctly")
Signed-off-by: Sasha Levin <sashal@kernel.org>