pc1crypt: make decrypt/encrypt functions take void * as argument

pc1crypt: make decrypt/encrypt functions take void * as argument

Make them more generic regarding accepted data buffers.

This fixes:

src/pc1crypt.c: In function ‘main’:
src/pc1crypt.c:322:26: warning: pointer targets in passing argument 2 of ‘pc1_decrypt_buf’ differ in signedness [-Wpointer-sign]
    pc1_decrypt_buf(&pc1, buf, datalen);
                          ^~~
src/pc1crypt.c:324:26: warning: pointer targets in passing argument 2 of ‘pc1_encrypt_buf’ differ in signedness [-Wpointer-sign]
    pc1_encrypt_buf(&pc1, buf, datalen);
                          ^~~

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>