optimize fp8 tile sizes for headdim 64 for faster fp8 decoding

Signed-off-by: Jonas Kuebler <kuebj@amazon.com>

Author: jmkuebler

hopper/tile_size.h

@@ -52,7 +52,10 @@ constexpr std::tuple<int, int, bool, bool> tile_size_fwd_sm90(
         }
     } else {
         if (headdim <= 64) {
-            return {192, 160, true, true};
+            if (use_one_mma_wg) {
+                return {64, 128, true, true};
+            } else {
+                return {192, 160, true, true};
         } else if (headdim <= 96) {
             return {192, 128, true, true};
         } else if (headdim <= 128) {