ata: pata_parport-bpck6: merge ppc6_rd_port16_blk into bpck6_read_block

ppc6_rd_port16_blk is only called by bpck6_read_block. Merge
ppc6_rd_port16_blk into bpck6_read_block.

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