usb: dummy_hcd: use HUB_CHAR_*

Fix  using the  bare numbers to set the 'wHubCharacteristics' field of the Hub
Descriptor while the values are #define'd in <linux/usb/ch11.h>.

Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>