EAP-pwd: Avoid double-frees on some error paths

EAP-pwd: Avoid double-frees on some error paths

At least some error paths (e.g., hitting the limit on hunt-and-peck
iterations) could have resulted in double-freeing of some memory
allocations. Avoid this by setting the pointers to NULL after they have
been freed instead of trying to free the data structure in a location
where some external references cannot be cleared. [Bug 453]

Signed-hostap: Jouni Malinen <j@w1.fi>