driver core: Drop unneeded 'extern' keyword in fwnode.h

driver core: Drop unneeded 'extern' keyword in fwnode.h

We do not use 'extern' keyword with functions. Remove the last one
mistakenly added to fwnode.h.

Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Saravana Kannan <saravanak@google.com>
Acked-by: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20240301180138.271590-2-andriy.shevchenko@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>