Fixes typo when indexing after self.conv1d

[tdgfrost]

Addresses two errors when use_eff_mem_path is set to False (to avoid causal_conv1d):

1. There is a typo at line 233 - currently the class references self.dconv (which doesn't exist) instead of self.d_conv. This gives rise to an attribute missing error.
2. Assuming I've understood correctly, the original code indexes the post-conv1d tensor incorrectly. For example, if the sequence length were 20 and the post-conv1d tensor has length 23, it is indexed to the last 3 items rather than the first 20.