hostid: simplify the code (#11502)

Author: oech3

src/uu/hostid/src/hostid.rs

@@ -21,10 +21,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
      * is a no-op unless unsigned int is wider than 32 bits.
      */
 
-    let mut result: c_long;
-    unsafe {
-        result = gethostid();
-    }
+    let mut result: c_long = unsafe { gethostid() };
 
     #[allow(overflowing_literals)]
     let mask = 0xffff_ffff;