llama : update llm_build_copy_mask_state comment

This commit updates the comment, which seems to contain a typo or be an
outdated comment, in the copy_mask_state function changing the variable
n_rs to n_kv.

I believe this change is correct and what the comment wants to
convey is to copy the states that are not going to be used in the
upcoming processing, which are the tokens states from n_seqs up to
the number of possible token states n_kv.

src/llama.cpp

@@ -9258,7 +9258,7 @@ static struct ggml_tensor * llm_build_copy_mask_state(
     // FIXME: zero-out NANs?
     states = ggml_mul(ctx, states, state_mask);
 
-    // copy states which won't be changed further (between n_seqs and n_rs)
+    // copy states which won't be changed further (between n_seqs and n_kv)
     ggml_build_forward_expand(graph,
         ggml_cpy(ctx,
             ggml_view_1d(ctx, states, n_state*(n_kv - n_seqs), n_seqs*n_state*ggml_element_size(states)),