rusticl/memory: fix sampler argument size check

Not entirely sure why this hasn't caused any problems...

Cc: mesa-stable
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/30602>

src/gallium/frontends/rusticl/api/kernel.rs

@@ -367,7 +367,14 @@ fn set_kernel_arg(
                     return Err(CL_INVALID_ARG_SIZE);
                 }
             }
-            _ => {
+
+            KernelArgType::Sampler => {
+                if arg_size != std::mem::size_of::<cl_sampler>() {
+                    return Err(CL_INVALID_ARG_SIZE);
+                }
+            }
+
+            KernelArgType::Constant => {
                 if arg.size != arg_size {
                     return Err(CL_INVALID_ARG_SIZE);
                 }