Commit ee2a0988 missed updating the comments for helper bpf_get_stack
in tools/include/uapi/linux/bpf.h. Sync it.

Fixes: ee2a0988 ("bpf: Adjust BPF stack helper functions to accommodate skip > 0")
Signed-off-by: Geliang Tang <geliang.tang@suse.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/ce54617746b7ed5e9ba3b844e55e74cb8a60e0b5.1648110794.git.geliang.tang@suse.com