Cast q.get_device() to char to avoid compiler warning (narrowing)

csrc/flash_attn/fmha_api.cpp

@@ -253,7 +253,8 @@ mha_fwd(const at::Tensor &q,         // total_q x num_heads x head_size, total_q
     bool loop = max_seqlen_k > blocksize_c;
 
     // Otherwise the kernel will be launched from cuda:0 device
-    at::cuda::CUDAGuard device_guard{q.get_device()};
+    // Cast to char to avoid compiler warning about narrowing
+    at::cuda::CUDAGuard device_guard{(char)q.get_device()};
 
     auto opts = q.options();
 
@@ -412,7 +413,8 @@ mha_bwd(const at::Tensor &dout,  // total_q x num_heads, x head_size
     bool loop = max_seqlen_k > blocksize_c;
 
     // Otherwise the kernel will be launched from cuda:0 device
-    at::cuda::CUDAGuard device_guard{q.get_device()};
+    // Cast to char to avoid compiler warning about narrowing
+    at::cuda::CUDAGuard device_guard{(char)q.get_device()};
 
     // It's possible the softmax_lse_ from the fwd has a different length since blocksize_c could be different.
     auto softmax_lse = softmax_lse_.index({torch::indexing::Slice(), torch::indexing::Slice(), torch::indexing::Slice(torch::indexing::None, max_seqlen_q)}).contiguous();