usb: host: mips: sead3: Update for EHCI register structure.

One line fix after 'struct ehci_regs' definition was changed
in commit a46af4ebf9ffec35eea0390e89935197b833dc61 (USB: EHCI: define
extension registers like normal ones).

Signed-off-by: Steven J. Hill <sjhill@mips.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>