regulator: of_regulator: Add missing colon for rdev kerneldoc argument

Kerneldoc validation gets confused if syntax isn't "@.*: ".

Adding the missing colons squashes the following W=1 warnings:

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Rajendra Nayak <rnayak@ti.com>
Link: https://lore.kernel.org/r/20200708124832.3441649-3-lee.jones@linaro.org


Signed-off-by: Mark Brown <broonie@kernel.org>