cmd/compile/abi-internal.md: fix table format
cmd/compile/abi-internal.md: fix table format

The table was not rendered correctly because one line missed a
column.

Change-Id: I1373e4e9fb8b8f2dcd9fd0db339083362cce9b71
Reviewed-on: https://go-review.googlesource.com/c/go/+/319291
Trust: Cherry Mui <d62e63aa42ce272d7b6a5055d97e942b33a34679@google.com>
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>

cloudflare/go,CAFxX/go,golang/go,cloudflare/go,cloudflare/go,CAFxX/go,golang/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,CAFxX/go,cloudflare/go,golang/go,CAFxX/go,cloudflare/go,nawawi/go,CAFxX/go,nawawi/go,nawawi/go,cloudflare/go,golang/go,golang/go,golang/go,nawawi/go,nawawi/go,golang/go,nawawi/go,CAFxX/go,cloudflare/go,CAFxX/go,cloudflare/go