Merge pull request #1848 from YosysHQ/eddie/fix_dynslice

ast: simplify to fully populate dynamic slicing case transformation

tests/simple/dynslice.v

@@ -0,0 +1,12 @@
+module dynslice (
+    input clk ,
+    input [9:0] ctrl ,
+    input [15:0] din ,
+    input [3:0] sel ,
+    output reg [127:0] dout
+);
+always @(posedge clk)
+begin
+    dout[ctrl*sel+:16] <= din ;
+end
+endmodule