MAINTAINERS: Add reviewer for regulator irq_helpers

Add a reviewer entry for the regulator irq_helpers.

Signed-off-by: Matti Vaittinen <matti.vaittinen@fi.rohmeurope.com>
Link: https://lore.kernel.org/r/2a4286ed98fd69b2539919e6a3e84d2e9804b4da.1622628334.git.matti.vaittinen@fi.rohmeurope.com


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