MAINTAINERS: Add entry for devm helpers

Devm helper header containing small inline helpers was added.
Hans promised to maintain it.

Add Hans as maintainer and myself as designated reviewer.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/eec1797734e3d080662aa732c565ed4a3c261799.1616506559.git.matti.vaittinen@fi.rohmeurope.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>