fix incorrect pointer type and fix unused use

src/ffi/device.rs

@@ -31,7 +31,7 @@ impl Device {
         let mut id: i32 = 0;
         let id_ptr = std::ptr::addr_of_mut!(id);
         let ret = cpp!(unsafe [
-            id_ptr as "int"
+            id_ptr as "int*"
         ] -> i32 as "int" {
             return cudaGetDevice(id_ptr);
         });

src/ffi/ptr.rs

@@ -1,5 +1,3 @@
-use crate::device::DeviceId;
-
 /// Represents a device-local pointer. Pointers qualify as device-local if they refer to memory that
 /// lives on the device, and not on the host.
 ///