useless alpha parameter and wrong model key

[damianoimola]

1. The actual version of the code does not works properly: if you run the provided code with alpha=0.2 or alpha=0.8, the result is totally the same. I think the main problem is in the computation of pnp_attn_t and pnp_f_t, that should be

pnp_attn_t = int(self.config.ddim_steps * self.config.alpha)
pnp_f_t = int(self.config.ddim_steps * self.config.alpha)

2. moreover, the model blipdiffusion does not exists, instead I think you should use Salesforce/blipdiffusion.