Users of an optional device_reset that have CONFIG_RESET_CONTROLLER=n
will trigger compilation errors. Add a static inline stub to fix it.

[ Note: device_reset is unused and unusable because we have no reset
  controller implementing .reset. It's available in Linux though and
  apparently useful for shared resets, so it's left in ]

Signed-off-by: Ahmad Fatoum <ahmad@a3f.at>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>