[media] msi2500: rename namespace msi3101 => msi2500

Rename driver namespace according to current driver name. Old
msi3101 was name of reference design, msi2500 is name of chip
itself.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>