xhci: Remove sparse warning about cmd_status.

Sparse complains about the arguments to xhci_evaluate_context_result() and
xhci_configure_endpoint_result():

  CHECK   drivers/usb/host/xhci.c
drivers/usb/host/xhci.c:1647:53: warning: incorrect type in argument 3 (different signedness)
drivers/usb/host/xhci.c:1647:53:    expected int *cmd_status
drivers/usb/host/xhci.c:1647:53:    got unsigned int [usertype] *[assigned] cmd_status
drivers/usb/host/xhci.c:1648:50: warning: incorrect type in argument 3 (different signedness)
drivers/usb/host/xhci.c:1648:50:    expected int *cmd_status
drivers/usb/host/xhci.c:1648:50:    got unsigned int [usertype] *[assigned] cmd_status

The command status is taken from the command completion event TRB, and
will always be a positive number.  Change the signature of
xhci_evaluate_context_result() and xhci_configure_endpoint_result() to
take a u32 for cmd_status.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>