usb: Fix compiler warning with gcc4.4

ehci-hcd.c: In function 'ehci_submit_root':
ehci-hcd.c:719: warning: value computed is not used
ehci-hcd.c:748: warning: value computed is not used

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Remy Bohmer <linux@bohmer.net>