Staging: dwc2: Fix conditional statement since urb->actual_length is never less than zero.

This patch fixes the following smatch warning in hcd.c:
drivers/staging/dwc2/hcd.c:787 dwc2_assign_and_init_hc() warn: unsigned 'urb->actual_length' is never less than zero.

Signed-off-by: Rashika Kheria <rashika.kheria@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>