regulator: lp87565: Use bitfield helpers

Use the FIELD_PREP() helper, instead open-coding the same operation.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://msgid.link/r/5e8781d31c983caf6bdabe36c5552077422cb8da.1708002575.git.geert+renesas@glider.beSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/lp87565-regulator.c

@@ -5,6 +5,7 @@
  * Copyright (C) 2017 Texas Instruments Incorporated - https://www.ti.com/
  */
 
+#include <linux/bitfield.h>
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/regmap.h>
@@ -99,7 +100,7 @@ static int lp87565_buck_set_ramp_delay(struct regulator_dev *rdev,
 
 	ret = regmap_update_bits(rdev->regmap, regulators[id].ctrl2_reg,
 				 LP87565_BUCK_CTRL_2_SLEW_RATE,
-				 reg << __ffs(LP87565_BUCK_CTRL_2_SLEW_RATE));
+				 FIELD_PREP(LP87565_BUCK_CTRL_2_SLEW_RATE, reg));
 	if (ret) {
 		dev_err(&rdev->dev, "SLEW RATE write failed: %d\n", ret);
 		return ret;