Hash is not passed from PSS methods to MGF1

[GrosQuildu]

The mgf1 method takes hash_class argument with default sha1 value.

python-pkcs1/pkcs1/mgf.py

Line 5 in 2492f80

def mgf1(mgf_seed, mask_len, hash_class=hashlib.sha1):

The PSS encode method also takes hash_class argument, but does not pass it down to the `mgf1:

python-pkcs1/pkcs1/emsa_pss.py

Line 43 in 2492f80

db_mask = mgf(h, em_len - h_len - 1)

Fix: pass the hash_class from top methods (like PSS encode and verify) to mgf1.