[media] radio-si470x: Always report support for RDS

The si470x i2c and usb driver support the RDS, so this ifdef statement
doesn't need more.

[mchehab@redhat.com: Fix a conflict on it]
Signed-off-by: Joonyoung Shim <jy0922.shim@samsung.com>
Acked-by: Tobias Lorenz <tobias.lorenz@gmx.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>