[MISC][AMD] Add unused annotation to rocm kernel file (#17097)

Signed-off-by: Lu Fang <lufang@fb.com>

csrc/rocm/skinny_gemms.cu

@@ -150,7 +150,7 @@ __global__ void LLGemm1_kernel(const scalar_t* in_a, const scalar_t* in_b,
   colB_elem4w = bf4[threadid * 4 + 3];
 
   scalar2_t Af2;
-  scalar2_t Bf2;
+  [[maybe_unused]] scalar2_t Bf2;
   float2 S;
 
   auto Ah2ptr = reinterpret_cast<scalar2_t*>(&rowA_elem4);
@@ -1597,4 +1597,4 @@ void wvSplitKQ(at::Tensor& in_a, at::Tensor& in_b, at::Tensor& out_c,
       }
     });
   });
-}
+}