glsl: Fix broadcast_index of lower_variable_index_to_cond_assign.

It's trying to get an int smeared across all channels, not trying to
get a 1:1 mapping of a subset of a vector's channels.  This usually
ended up not mattering with ir_to_mesa, since it just smears floats
into every chan of a vec4.

Fixes:
glsl1-temp array with swizzled variable indexing

src/glsl/lower_variable_index_to_cond_assign.cpp

@@ -117,7 +117,7 @@ struct switch_generator
 	    new(this->mem_ctx) ir_dereference_variable(index);
 
          if (comps) {
-	    const ir_swizzle_mask m = { 0, 1, 2, 3, comps, false };
+	    const ir_swizzle_mask m = { 0, 0, 0, 0, comps, false };
 	    broadcast_index = new(this->mem_ctx) ir_swizzle(broadcast_index, m);
 	 }