EHCI: fix root hub device descriptor

On little endian machines, EHCI root hub's USB revision is reported as 0.2 --
cpu_to_le16() was missed in the initializer for the 'bcdUSB' descriptor field.
The same should be done for the 'bcdDevice' field.

Signed-off-by: Sergei Shtylyov <sshtylyov@mvista.com>