xhci: Put warning message on a single line

This allows someone to grep for the complete warning message as in;
xhci-hcd xhci-hcd.0.auto: USB core suspending device not in U0/U1/U2.

Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>