regmap: trivial comment fix (copy'n'paste error)

fix a trivial copy'n'paste error in the regmap kerneldoc, s/write/read/
for the regmap_read(), regmap_raw_read() and regmap_bulk_read() routines

Signed-off-by: Gerhard Sittig <gsi@denx.de>
Signed-off-by: Mark Brown <broonie@linaro.org>