aya: fix create pinned map path.

`MapData::create_pinned` is supposed to call `map.pin`(BPF_OBJ_PIN) if
`BPF_OBJ_GET` syscall return error, but it joins `name` redundantly,
making `path/map_name` to be `path/map_name/map_name`.This
commit fixed it.

aya/src/maps/mod.rs

@@ -490,7 +490,6 @@ impl MapData {
             }
             Err(_) => {
                 let mut map = Self::create(obj, name, btf_fd)?;
-                let path = path.join(name);
                 map.pin(&path).map_err(|error| MapError::PinError {
                     name: Some(name.into()),
                     error,