binder: cleanup `unsafe` in `unsafe fn`s warning (`E0133`)

[ojeda]

We enabled the warnings in #339 and we would like to move it to hard error, so we need to clean them up.

warning: call to unsafe function is unsafe and requires unsafe block (error E0133)
 --> drivers/android/node.rs:86:20
 |
86 | inner: SpinLock::new(NodeDeathInner {
 | ____________________^
87 | | dead: false,
88 | | cleared: false,
89 | | notification_done: false,
90 | | aborted: false,
91 | | }),
 | |______________^ call to unsafe function