!7574 Modifiy nn.Matmul

Merge pull request !7574 from wanyiming/Mod_Matmul

mindspore/nn/layer/math.py

@@ -354,7 +354,6 @@ def check_col_row_equal(x1_shape, x2_shape, transpose_x1, transpose_x2):
                          + f'the row of matrix dimensions of x2, but got {x1_col} and {x2_row}.')
 
 
-@constexpr
 def matmul_op_select(x1_shape, x2_shape, transpose_x1, transpose_x2):
     """select matmul op"""
     x1_dim, x2_dim = len(x1_shape), len(x2_shape)