fix two minor clippy warnings

src/uu/dd/src/dd.rs

@@ -1181,7 +1181,7 @@ fn calc_loop_bsize(
             cmp::min(ideal_bsize as u64, rremain * ibs as u64) as usize
         }
         Some(Num::Bytes(bmax)) => {
-            let bmax: u128 = (*bmax).try_into().unwrap();
+            let bmax: u128 = (*bmax).into();
             let bremain: u128 = bmax - wstat.bytes_total;
             cmp::min(ideal_bsize as u128, bremain) as usize
         }

src/uu/tr/src/tr.rs

@@ -61,7 +61,7 @@ pub fn uumain(args: impl uucore::Args) -> UResult<()> {
         ));
     }
 
-    if let Some(first) = sets.get(0) {
+    if let Some(first) = sets.first() {
         if first.ends_with('\\') {
             show!(USimpleError::new(
                 0,