iio: dac: Convert to common field_prep() helper

Drop the driver-specific field_prep() macro, in favor of the globally
available variant from <linux/bitfield.h>.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Yury Norov (NVIDIA) <yury.norov@gmail.com>

Author: geertu

drivers/iio/dac/ad3530r.c

@@ -53,10 +53,6 @@
 #define AD3530R_MAX_CHANNELS			8
 #define AD3531R_MAX_CHANNELS			4
 
-/* Non-constant mask variant of FIELD_PREP() */
-#undef field_prep
-#define field_prep(_mask, _val)	(((_val) << (ffs(_mask) - 1)) & (_mask))
-
 enum ad3530r_mode {
 	AD3530R_NORMAL_OP,
 	AD3530R_POWERDOWN_1K,