Add explicit casts to satisfy g++ (#102)

Fixes warning / error from qcbor_decode.h
diff --git a/inc/qcbor/qcbor_decode.h b/inc/qcbor/qcbor_decode.h
index 1fcbc5d..94126bd 100644
--- a/inc/qcbor/qcbor_decode.h
+++ b/inc/qcbor/qcbor_decode.h
@@ -1281,12 +1281,12 @@
 
 static inline QCBORError QCBORDecode_GetError(QCBORDecodeContext *pMe)
 {
-    return pMe->uLastError;
+    return (QCBORError)pMe->uLastError;
 }
 
 static inline QCBORError QCBORDecode_GetAndResetError(QCBORDecodeContext *pMe)
 {
-    const QCBORError uReturn = pMe->uLastError;
+    const QCBORError uReturn = (QCBORError)pMe->uLastError;
     pMe->uLastError = QCBOR_SUCCESS;
     return uReturn;
 }