regulator: Fix documentation for of_node parameter of regulator_register()

Commit 5bc75a886353 ("kernel-doc: fix new warning in regulator core")
added documentation for of_node to address a warning but the
documentation didn't explain what the parameter is for so would be
likely to be unhelpful for users.  Clarify that.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/regulator/core.c

@@ -2731,7 +2731,8 @@ static void rdev_init_debugfs(struct regulator_dev *rdev)
  * @dev: struct device for the regulator
  * @init_data: platform provided init data, passed through by driver
  * @driver_data: private regulator data
- * @of_node: target open firmware device structure (may be NULL)
+ * @of_node: OpenFirmware node to parse for device tree bindings (may be
+ *           NULL).
  *
  * Called by regulator drivers to register a regulator.
  * Returns 0 on success.