regulator: max20411: Directly include bitfield.h

The max20411 driver uses bitfield.h but does not directly include
it, add an inclusion to avoid build errors in configurations
which do not result in an implicit inclusion.
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/max20411-regulator.c

@@ -4,6 +4,7 @@
  * Copyright (c) 2022, Linaro Ltd.
  */
 
+#include <linux/bitfield.h>
 #include <linux/gpio/consumer.h>
 #include <linux/i2c.h>
 #include <linux/module.h>