Fixes template parameter order in flash backward kernel

Corrects the template parameter list by removing an extra `false` parameter
that was causing compilation issues or incorrect behavior in the kernel traits
instantiation for devices with limited shared memory.

Author: LoserCheems

csrc/src/flash_bwd_launch_template.h

@@ -274,7 +274,7 @@ void run_mha_bwd_hdim256(Flash_bwd_params &params, cudaStream_t stream) {
     } else if (max_smem_per_block >= 144 * 1024) {  // A100, we don't do double buffering to save smem
         run_flash_bwd<Flash_bwd_kernel_traits<Headdim, 64, 64, 8, 4, 2, 2, false, true, T>, Is_causal>(params, stream);
     } else { // sm86 and sm89, max smem is 99 KB. V in regs and no double buffering.
-        run_flash_bwd<Flash_bwd_kernel_traits<Headdim, 64, 32, 8, 4, 1, 2, true, true, T>, false, Is_causal>(params, stream);
+        run_flash_bwd<Flash_bwd_kernel_traits<Headdim, 64, 32, 8, 4, 1, 2, true, true, T>, Is_causal>(params, stream);
     }
 }