musb_hdrc: Fixes before pulling from mainline tree

Latest musb_hdrc code wouldn't:
  * build ... because there's now a standard WARN() macro
  * build without false printf format warnings ... "%zd" is for ssize_t,
    while "%zu" is for size_t

Signed-off-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>