driver core: property: Update fwnode_property_read_string_array()

Commit 5c0acf3b (driver core: Add comments about returning array
counts) forgot to update fwnode_property_read_string_array() along
the lines of device_property_read_string_array(), although it did
change the kerneldoc comment of it.  Fix that.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>