Re-factor DescriptorSecretKey::to_public

Do minor refactor to the `to_public` method on `DesciptorSecretKey`.

Re-factor only, no logic changes.

Author: tcharding

src/descriptor/key.rs

@@ -254,14 +254,14 @@ impl DescriptorSecretKey {
         &self,
         secp: &Secp256k1<C>,
     ) -> Result<DescriptorPublicKey, DescriptorKeyParseError> {
-        Ok(match self {
-            &DescriptorSecretKey::SinglePriv(ref sk) => {
-                DescriptorPublicKey::SinglePub(sk.to_public(secp)?)
-            }
-            &DescriptorSecretKey::XPrv(ref xprv) => {
-                DescriptorPublicKey::XPub(xprv.to_public(secp)?)
+        let pk = match self {
+            DescriptorSecretKey::SinglePriv(prv) => {
+                DescriptorPublicKey::SinglePub(prv.to_public(secp))
             }
-        })
+            DescriptorSecretKey::XPrv(xprv) => DescriptorPublicKey::XPub(xprv.to_public(secp)?),
+        };
+
+        Ok(pk)
     }
 }