OMAPDSS: HDMI5: Fix AUDICONF3 bitfield offsets

Downmix inhibit in HDMI_CORE_FC_AUDICONF3 register is in
bit 4 while CEA861_AUDIO_INFOFRAME_DB5_DM_INH sets bit 7.

Signed-off-by: Misael Lopez Cruz <misael.lopez@ti.com>
Signed-off-by: Jyri Sarha <jsarha@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>