ata: pata_sil680: Add some missing function parameter docs

ata: pata_sil680: Add some missing function parameter docs

Fixes the following W=1 kernel build warning(s):

 drivers/ata/pata_sil680.c:68: warning: Function parameter or member 'adev' not described in 'sil680_seldev'
 drivers/ata/pata_sil680.c:254: warning: Function parameter or member 'try_mmio' not described in 'sil680_init_chip'

Cc: Jens Axboe <axboe@kernel.dk>
Cc: Andre Hedrick <andre@linux-ide.org>
Cc: Red Hat <alan@redhat.com>
Cc: linux-ide@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20210318085150.3131936-3-lee.jones@linaro.org
Signed-off-by: Jens Axboe <axboe@kernel.dk>