ata: pata_parport-bpck6: merge ppc6_wr_port into bpck6_write_regr

ppc6_wr_port is only called by bpck6_write_regr. Merge ppc6_wr_port
into bpck6_write_regr.

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