USB: xhci: Remove obsolete debugging printk.

When code to manipulate the command register was refactored from
xhci_run() to xhci_start(), a debugging statement was left behind that no
longer applies.  Remove that statement.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Reported-by: Sergei Shtylyov <sshtylyov@mvista.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>