USB: dummy-hcd: use usb_urb_dir_in instead of usb_pipein

Commit fea34091 ("USB: add direction bit to urb->transfer_flags") has
added a usb_urb_dir_in() helper function that can be used to determine
the direction of the URB. With that patch USB_DIR_IN control requests with
wLength == 0 are considered out requests by real USB HCDs. This patch
changes dummy-hcd to use the usb_urb_dir_in() helper to match that
behavior.

Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>