[V1] Fix wrong import path of get_flash_attn_version (#15280)

Signed-off-by: Lehua Ding <lehuading@tencent.com>

vllm/v1/attention/backends/mla/common.py

@@ -195,8 +195,8 @@ from vllm import _custom_ops as ops
 from vllm.attention.backends.abstract import (AttentionBackend, AttentionLayer,
                                               AttentionMetadata,
                                               MLAAttentionImpl)
-from vllm.attention.backends.utils import get_flash_attn_version
 from vllm.attention.ops.triton_merge_attn_states import merge_attn_states
+from vllm.fa_utils import get_flash_attn_version
 from vllm.logger import init_logger
 from vllm.model_executor.layers.linear import (ColumnParallelLinear,
                                                LinearBase, RowParallelLinear,