fix(mlir): use ptr_type for sol.alloca alloc_type attribute (#340)

The `alloc_type` attribute on `sol.alloca` was set to `element_type`,
but the TableGen custom builder uses the same type for both `alloc_type`
and the result (`Sol_PtrType`). This sets it to `ptr_type` to match the
ODS definition.

Author: hedgar2017

solx-mlir/src/context/builder.rs

@@ -801,7 +801,7 @@ impl<'context> Builder<'context> {
         block
             .append_operation(
                 AllocaOperation::builder(self.context, self.unknown_location)
-                    .alloc_type(TypeAttribute::new(element_type))
+                    .alloc_type(TypeAttribute::new(ptr_type))
                     .addr(ptr_type)
                     .build()
                     .into(),