Remove mistaken & from code example in MAP_TYPE_ARRAY docs

Fixes: 1cfa97b3 ("bpf, docs: Document BPF_MAP_TYPE_ARRAY")
Signed-off-by: Donald Hunter <donald.hunter@gmail.com>
Link: https://lore.kernel.org/r/20221115095910.86407-1-donald.hunter@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>