ata: pata_parport-bpck6: merge ppc6_wr_port16_blk into bpck6_write_block

ppc6_wr_port16_blk is only called by bpck6_write_block. Merge
ppc6_wr_port16_blk into bpck6_write_block.

Signed-off-by: Ondrej Zary <linux@zary.sk>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>