usb: xhci: Cleanup printk debug message for registers

The content of each register has been exposed through debugfs.
There is no need to dump register content with printk in code
lines. Remove them to make code more concise and readable.

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>