gpio: bd7xxxx: use helper variable for pdev->dev

Using a helper local variable to store the address of &pdev->dev adds
to readability and allows us to avoid unnecessary line breaks.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Reviewed-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>