Fix below warning when CONFIG_OF=n:

drivers/regulator/rt4801-regulator.c:206:34: warning: unused variable 'rt4801_of_id' [-Wunused-const-variable]
  206 | static const struct of_device_id rt4801_of_id[] = {
      |                                  ^~~~~~~~~~~~
Signed-off-by: ChiYuan Huang <cy_huang@richtek.com>
Reported-by: kernel test robot <lkp@intel.com>
Link: https://lore.kernel.org/r/1598234713-8532-1-git-send-email-u0084500@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>