ax(ueps): fix tlvError comment to show type usage, not sentinel usage

The comment was a duplicate of errTLVValueTooLarge's example.
Fixed to show how tlvError defines new sentinels.

Co-Authored-By: Charon <charon@lethean.io>

pkg/ueps/packet.go

@@ -12,7 +12,7 @@ import (
 // if errors.Is(err, errTLVValueTooLarge) { /* value exceeded 255-byte TLV length limit */ }
 var errTLVValueTooLarge = tlvError("TLV value too large for 1-byte length header")
 
-// writeTLV(buf, TagPayload, oversized) → errTLVValueTooLarge
+// var errMyError = tlvError("my error message")
 type tlvError string
 
 func (e tlvError) Error() string { return string(e) }