xhci: make warnings greppable

This changes debug messages and warnings in xhci-ring.c
to be on a single line so grep can find them. grep must
have precedence over the 80 column limit.

[Sarah fixed two checkpatch.pl issues with split lines
introduced by this commit.]

Signed-off-by: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>