bpftool: Don't drop a type in the sorted C dump

The C dump sorts types by default, so that generated headers are
diffable. The sorted dump emits one type fewer than the unsorted dump
of the same BTF.

dump_btf_c() starts its loop at index 1 to skip the void type at BTF
type ID 0. That holds for the unsorted dump, where the array index is
the type ID, but not after qsort(): position 0 is then the lowest
ranked type, and btf_type_rank() ranks an anonymous enum 0 while void
takes the default rank of 10. So the enum is skipped, and void is
emitted instead as a no-op.

Fixes: 94133cf24bb3 ("bpftool: Introduce btf c dump sorting")
Acked-by: Eduard Zingerman <eddyz87@gmail.com>
Signed-off-by: Ihor Solodrai <ihor.solodrai@linux.dev>
Link: https://lore.kernel.org/r/20260828215207.3105313-7-ihor.solodrai@linux.dev
Signed-off-by: Alexei Starovoitov <ast@kernel.org>