Fix use usages

Author: yesh0

src/lib.rs

@@ -13,7 +13,6 @@
 //! - Interrupt manipulation mechanisms.
 //! - Wrappers around assembly instructions like `WFI`.
 
-
 #![no_std]
 #[macro_use]
 extern crate bitflags;

src/register/satp.rs

@@ -1,7 +1,7 @@
 //! satp register
 
 #[cfg(riscv)]
-use addr::Frame;
+use crate::addr::Frame;
 use bit_field::BitField;
 
 /// satp register