[media] tda7432: Fix setting TDA7432_MUTE bit for TDA7432_RF register

Fix a copy-paste bug when converting to the control framework.

Fixes: commit 5d478e0d ("[media] tda7432: convert to the control framework")

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>