misc: block: drop extern crate, use modern rust

This commit is part of a series of similar commits.

Signed-off-by: Philipp Schuster <philipp.schuster@cyberus-technology.de>
On-behalf-of: SAP philipp.schuster@sap.com

block/src/raw_sync.rs

@@ -7,6 +7,7 @@ use std::fs::File;
 use std::io::{Seek, SeekFrom};
 use std::os::unix::io::{AsRawFd, RawFd};
 
+use log::warn;
 use vmm_sys_util::eventfd::EventFd;
 
 use crate::DiskTopology;