misc/silicon: fix build on ARM / POWER
error[E0308]: mismatched types
--> src/hb_wrapper.rs:17:17 |
16 | hb_feature_from_string(
| ---------------------- arguments to this function are incorrect
17 | tag.as_ptr() as *const i8,
| ^^^^^^^^^^^^^^^^^^^^^^^^^ expected `u8`, found `i8`
|
= note: expected raw pointer `*const u8`
found raw pointer `*const i8`