usb: doc: hotplug.txt code typos

Fixed several typos in the code examples given in
Documentation/usb/hotplug.txt.

  - missing [] with array of struct usb_device_id

  - checkpatch.pl warning: space between function name and parenthesis

  - missing terminating ';'

Signed-off-by: Jeremiah Mahler <jmmahler@gmail.com>