xhci: Remove debugging about ring structure allocation.

Debuggers only really care what the xHCI driver sets the ring dequeue
pointer to, so make the driver stop babbling about the memory addresses
of internal ring structures.  This makes wading through the output of
allocating and freeing 256 stream rings much easier by reducing the
number of output lines per ring from 9 to 1.

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