usb: xhci: remove xhci_dbg_ctx()

XHCI context changes have already been traced by the trace
events. It's unnecessary to put the same message in kernel
log. This patch removes the use of xhci_dbg_ctx().

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>