Symbolic shape inference: fix a bug in shape merge (#5519)
* Symbolic shape inference: fix a bug in shape merge
OpType Where:
input0: ['mt_src_tokens_batch', 1, 1, 'mt_src_tokens_len']
input1: []
input2: ['mt_prev_output_tokens_batch', 12, 'mt_prev_output_tokens_len', 'floor(mt_src_tokens_batch*mt_src_tokens_len/mt_prev_output_tokens_batch)'] 1
output: [None, 12, 'mt_prev_output_tokens_len', None]
* Undo unintended TRT change
