gpio: vf610: Don't use explicit &pdev->dev in vf610_gpio_probe()

The code already defines "dev" variable to help with that, so make
sure all of the code uses it.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Andrew Lunn <andrew@lunn.ch>
Cc: Heiner Kallweit <hkallweit1@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: linux-gpio@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-imx@nxp.com
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>