`os_perso_derive_node_with_seed_key` doesn't match OS behavior for `HDW_SLIP21`

[bigspider]

If the path is composed of multiple SLIP-21 derivation steps, the current OS parses using the '/' character as a separator.

Speculos, instead, currently treats the whole path argument as a single derivation step. Therefore, they don't match if there is more than one derivation step.