[media] MAINTAINERS: add msi3101 driver

Mirics MSi2500 (MSi3101) SDR ADC + USB interface driver. Currently
in staging as SDR API is not ready.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Acked-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>