eth: replace fw error with data error in verify function

closes #422

src/apps/ethereum/verify_message.py

@@ -1,5 +1,6 @@
 from ubinascii import hexlify
 
+from trezor import wire
 from trezor.crypto.curve import secp256k1
 from trezor.crypto.hashlib import sha3_256
 from trezor.messages.Success import Success
@@ -22,12 +23,12 @@ async def verify_message(ctx, msg):
     pubkey = secp256k1.verify_recover(sig, digest)
 
     if not pubkey:
-        raise ValueError("Invalid signature")
+        raise wire.DataError("Invalid signature")
 
     pkh = sha3_256(pubkey[1:], keccak=True).digest()[-20:]
 
     if msg.address != pkh:
-        raise ValueError("Invalid signature")
+        raise wire.DataError("Invalid signature")
 
     address = "0x" + hexlify(msg.address).decode()