ata: pata_parport-bpck6: Declare mode_map as static

Compilation C=1 of the bpck6 protocol module generates the following
message:

drivers/ata/pata_parport/bpck6.c:62:5: warning: symbol 'mode_map' was
not declared. Should it be static?

Fix this by declaring mode_map as static.

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