Fix profiling for Keras LSTM layers.

[Landay7]

Description

Before it for Keras LSTM it throws IndexError: list index out of range.
I know, that there is a low chance that it will be run without the HLS model, but still would be good to set properly.

Type of change

• Bug fix (non-breaking change that fixes an issue)

Tests

import hls4ml
from tensorflow.keras.models import Model
from tensorflow.keras.layers import Conv1D, Activation, MaxPooling1D, LSTM, Dense, Input

input = Input(shape = (600, 10 ), name = 'input')
    
x = Conv1D(
    filters = 4,
    kernel_size = 3,
    strides = 1,
    padding = 'valid',
    name = 'conv_1',
)(input)

x = Activation(
    'relu',
    name = 'conv_act_1'
)(x)
x = MaxPooling1D(
    pool_size = 3,
    padding = 'valid',
    name = 'pool_1'
)(x)
x = LSTM(16, name = 'lstm')(x)
x = Dense(10, name = 'dense')(x)

model = Model(inputs = input, outputs = x)
hls4ml.model.profiling.numerical(model = model, hls_model = None)

Checklist

• I have read the guidelines for contributing.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• My changes generate no new warnings.
• I have installed and run pre-commit on the files I edited or added.
• I have added tests that prove my fix is effective or that my feature works.