Fix res_ty for rc_annot
Without this MR code like
u16 rateval = rc_bitfield_init(u16, "rate_sig");
generates
f_code := (
<[ "#0" :=
"rateval" <-{ IntOp u16 }
LocInfoE loc_708 (UnOp (CastOp $ IntOp u16) (IntOp i32) (LocInfoE loc_708 (AnnotExpr 1%nat (BitfieldInitAnnot (rate_sig)) (LocInfoE loc_709 (UnOp (CastOp $ IntOp u16) (IntOp i32) (LocInfoE loc_710 (i2v 0 i32))))))) ;
Note that this contains a cast too much.
This MR fixes this issue and a similar issue for the ternary operator.
@lepigre Does this fix make sense?