Fix PTI compilation

It's broken on master anyway

src/arch/x86_64/gdt.rs

@@ -99,7 +99,7 @@ pub unsafe fn set_tcb(pid: usize) {
 
 #[cfg(feature = "pti")]
 pub unsafe fn set_tss_stack(stack: usize) {
-    use arch::x86_64::pti::{PTI_CPU_STACK, PTI_CONTEXT_STACK};
+    use super::pti::{PTI_CPU_STACK, PTI_CONTEXT_STACK};
     TSS.rsp[0] = (PTI_CPU_STACK.as_ptr() as usize + PTI_CPU_STACK.len()) as u64;
     PTI_CONTEXT_STACK = stack;
 }

src/arch/x86_64/pti.rs

@@ -2,11 +2,11 @@
 use core::ptr;
 
 #[cfg(feature = "pti")]
-use memory::Frame;
+use crate::memory::Frame;
 #[cfg(feature = "pti")]
-use paging::ActivePageTable;
+use crate::paging::ActivePageTable;
 #[cfg(feature = "pti")]
-use paging::entry::EntryFlags;
+use crate::paging::entry::EntryFlags;
 
 #[cfg(feature = "pti")]
 #[thread_local]