clippy: fix the match_wildcard_for_single_variants lint

Better to be explicit.

Author: apoelstra

src/pset/serialize.rs

@@ -227,7 +227,7 @@ impl Serialize for confidential::Value {
         match self {
             confidential::Value::Null => vec![], // should never be invoked
             confidential::Value::Explicit(x) => Serialize::serialize(x),
-            y => encode::serialize(y), // confidential can serialized as is
+            confidential::Value::Confidential(_) => encode::serialize(self), // confidential can serialized as is
         }
     }
 }
@@ -272,7 +272,7 @@ impl Serialize for confidential::Asset {
         match self {
             confidential::Asset::Null => vec![], // should never be invoked
             confidential::Asset::Explicit(x) => Serialize::serialize(x),
-            y => encode::serialize(y), // confidential can serialized as is
+            confidential::Asset::Confidential(_) => encode::serialize(self), // confidential can serialized as is
         }
     }
 }

src/sighash.rs

@@ -180,7 +180,7 @@ impl<T> Prevouts<'_, T> where T: Borrow<TxOut> {
     fn get_all(&self) -> Result<&[T], Error> {
         match self {
             Prevouts::All(prevouts) => Ok(*prevouts),
-            _ => Err(Error::PrevoutKind),
+            Prevouts::One(..) => Err(Error::PrevoutKind),
         }
     }