regulator: wm8400: Get rid of wm8400_block_read/wm8400_set_bits functions

The only user of wm8400_block_read/wm8400_set_bits functions is the
wm8400 regulator driver. At the context of all the callers, we can
use regmap_bulk_read/regmap_update_bits directly.
Thus remove wm8400_block_read/wm8400_set_bits functions.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Signed-off-by: Mark Brown <broonie@kernel.org>