common : fix typo in speculative.cpp comment [no ci] (#28750)

common/speculative.cpp

@@ -1493,7 +1493,7 @@ struct common_speculative_impl_draft_mtp : public common_speculative_impl {
 
         const int32_t n_tokens = batch_in.n_tokens;
 
-        // remember the frist and last batch index for each sequence
+        // remember the first and last batch index for each sequence
         std::fill(i_batch_beg.begin(), i_batch_beg.end(), -1);
         std::fill(i_batch_end.begin(), i_batch_end.end(), -1);