eina: Fixed undefined behavior usage of bitfields and enumerations

On Microsoft Visual Studio, enumerations are signed and consequently get sign-extended when used with bit-fields, which causes the number to become inadvertently negative.

I removed the undefined behavior use by defining explictly as a unsigned int, so it works on all platforms.

src/lib/eina/eina_rbtree.c

@@ -61,7 +61,7 @@ struct _Eina_Iterator_Rbtree_List
 {
    Eina_Rbtree *tree;
 
-   Eina_Rbtree_Direction dir : 1;
+   unsigned int dir : 1;
    Eina_Bool up : 1;
 };