usb: ohci-da8xx: add a helper pointer to &pdev->dev

Add a helper pointer to &pdev->dev. This improves readability by
removing all the &pdev->dev dereferencing.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>