ata: pata_artop: remove redundant initialization of pio

pio is initialized and the data is never read, instead it is almost
immediately being updated to a new value. Fix this by removing the
initialization.

Detected by scan-build:
"warning: Value stored to 'pio' during its initialization is never read"

Fixes: 669a5db4 ("[libata] Add a bunch of PATA drivers")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Tejun Heo <tj@kernel.org>