block/rc2: update test for new bswap signatures

test/block/rc2.cpp

@@ -104,7 +104,7 @@ int main ()
             std::begin (plain),
             std::end   (plain),
             std::begin (plain),
-            cruft::bswap<u16>
+            static_cast<u16(&)(u16)> (cruft::bswap)
         );
 
         std::array<u16,4> cipher = t.cipher;
@@ -112,7 +112,7 @@ int main ()
             std::begin (cipher),
             std::end   (cipher),
             std::begin (cipher),
-            cruft::bswap<u16>
+            static_cast<u16(&)(u16)> (cruft::bswap)
         );
 
         tap.expect (obj.encrypt (plain) == cipher, "rc2_enc");