rust_binder: use `core::ffi::CStr` method names

Prepare for `core::ffi::CStr` taking the place of `kernel::str::CStr` by
avoiding methods that only exist on the latter.

This backslid in commit eafedbc7c050 ("rust_binder: add Rust Binder
driver").

Reviewed-by: Alice Ryhl <[e-mail]>
Signed-off-by: Tamir Duberstein <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Miguel Ojeda <[e-mail]>

drivers/android/binder/stats.rs

···
         // SAFETY: Accessing `binder_command_strings` is always safe.
         let c_str_ptr = unsafe { binder_command_strings[i] };
         // SAFETY: The `binder_command_strings` array only contains nul-terminated strings.
-        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.as_bytes();
+        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.to_bytes();
         // SAFETY: The `binder_command_strings` array only contains strings with ascii-chars.
         unsafe { from_utf8_unchecked(bytes) }
     }
···
         // SAFETY: Accessing `binder_return_strings` is always safe.
         let c_str_ptr = unsafe { binder_return_strings[i] };
         // SAFETY: The `binder_command_strings` array only contains nul-terminated strings.
-        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.as_bytes();
+        let bytes = unsafe { CStr::from_char_ptr(c_str_ptr) }.to_bytes();
         // SAFETY: The `binder_command_strings` array only contains strings with ascii-chars.
         unsafe { from_utf8_unchecked(bytes) }
     }