No accuracy in Keras RNN Model with Bitcoin Data
Remember, accuracy is a classification measure. That is, it's used to evaluate models that attempt to predict membership in one of a few discrete values. No accuracy in this case means that you haven't predicted and values exactly correctly- a pretty common occurance in regression problems- that is, problems that measure the scale of a phenomenon or "how much" of something happens. 

A better metric to evaluate your regression model might be MSE, such as used for your function.

Try:

    # Compile model
model.compile(
    loss='mse',
    optimizer='adam',
    metrics=['mse'],
)