of: constify drv arg of of_driver_match_device stub

of: constify drv arg of of_driver_match_device stub

With this change the stub has the same signature as the actual function,
preventing this compiler warning when building without CONFIG_OF:

   drivers/base/property.c: In function 'fwnode_driver_match_device':
>> drivers/base/property.c:608:38: warning: passing argument 2 of 'of_driver_match_device' discards 'const' qualifier from pointer target type
      return of_driver_match_device(dev, drv);
                                         ^
   In file included from drivers/base/property.c:18:0:
   include/linux/of_device.h:61:19: note: expected 'struct device_driver *' but argument is of type 'const struct device_driver *'
    static inline int of_driver_match_device(struct device *dev,
                      ^

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>