fs: copy: Use File::set_permissions instead of fs::set_permissions

We already got the open file descriptor at this point.
Don't make the kernel resolve the path again.

src/libstd/sys/unix/fs.rs

@@ -807,14 +807,14 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     let perm = reader.metadata()?.permissions();
 
     let ret = io::copy(&mut reader, &mut writer)?;
-    set_permissions(to, perm)?;
+    writer.set_permissions(perm)?;
     Ok(ret)
 }
 
 #[cfg(any(target_os = "linux", target_os = "android"))]
 pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
     use cmp;
-    use fs::{File, set_permissions};
+    use fs::File;
     use sync::atomic::{AtomicBool, Ordering};
 
     // Kernel prior to 4.5 don't have copy_file_range
@@ -886,14 +886,14 @@ pub fn copy(from: &Path, to: &Path) -> io::Result<u64> {
                         // Try again with fallback method
                         assert_eq!(written, 0);
                         let ret = io::copy(&mut reader, &mut writer)?;
-                        set_permissions(to, perm)?;
+                        writer.set_permissions(perm)?;
                         return Ok(ret)
                     },
                     _ => return Err(err),
                 }
             }
         }
     }
-    set_permissions(to, perm)?;
+    writer.set_permissions(perm)?;
     Ok(written)
 }