ohci: check device is not NULL before calling usb_ep_get()

A call to ohci_find_device() can return NULL if it doesn't find a
device matching 'addr' so for the two callers, explicitly check
the return value before passing it to usb_ep_get().

Signed-off-by: Liam Merwick <liam.merwick@oracle.com>
Message-id: 1549460216-25808-6-git-send-email-liam.merwick@oracle.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>