regulator: wm8400-regulator: Repair dodgy kerneldoc header formatting

W=1 kernel builds report a lack of descriptions for various
function arguments.  In reality they are documented, but the
formatting was not as expected '@.*:'.  Instead, some weird
arg identifiers were used.

This change fixes the following warnings:

 drivers/regulator/wm8400-regulator.c:243: warning: Function parameter or member 'dev' not described in 'wm8400_register_regulator'
 drivers/regulator/wm8400-regulator.c:243: warning: Function parameter or member 'reg' not described in 'wm8400_register_regulator'
 drivers/regulator/wm8400-regulator.c:243: warning: Function parameter or member 'initdata' not described in 'wm8400_register_regulator'

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Charles Keepax <ckeepax@opensource.cirrus.com>
Cc: patches@opensource.cirrus.com
Link: https://lore.kernel.org/r/20200626065738.93412-9-lee.jones@linaro.org
Signed-off-by: Mark Brown <broonie@kernel.org>