bpf: tcp: Remove comma which is causing build error

Currently, building the bpf-next source with the CONFIG_BPF_SYSCALL
enabled is causing a compilation error:

"net/ipv4/bpf_tcp_ca.c:209:28: error: expected identifier or '(' before
',' token"

Fix this by removing an unnecessary comma.

Fixes: e78aea8b21 ("bpf: tcp: Put some tcp cong functions in allowlist for bpf-tcp-cc")
Reported-by: syzbot+0b74d8ec3bf0cc4e4209@syzkaller.appspotmail.com
Signed-off-by: Atul Gopinathan <atulgopinathan@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20210328120515.113895-1-atulgopinathan@gmail.com

net/ipv4/bpf_tcp_ca.c

@@ -206,7 +206,7 @@ BTF_ID(func, bbr_init)
 BTF_ID(func, bbr_main)
 BTF_ID(func, bbr_sndbuf_expand)
 BTF_ID(func, bbr_undo_cwnd)
-BTF_ID(func, bbr_cwnd_even),
+BTF_ID(func, bbr_cwnd_even)
 BTF_ID(func, bbr_ssthresh)
 BTF_ID(func, bbr_min_tso_segs)
 BTF_ID(func, bbr_set_state)