usb: Increase timeout value for device reset

It seems that for USB IP on Freescale MX5x processors, it needs >750
usec for the reset to complete. This change should not hurt any other
EHCI hardware.

Signed-off-by: Dinh Nguyen <Dinh.Nguyen@freescale.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>