drm/radeon/hdmi: don't set SEND_MAX_PACKETS bit

Many TVs and A/V receivers don't work with this bit set. Problem was
confirmed using: Onkyo TX-SR605, Sony BRAVIA KDL-52X3500, Sony BRAVIA
KDL-40S40xx. In theory this bit shouldn't affect audio engine when
feeding it with data, however it seems it does. Driver fglrx doesn't set
that bit in any of the above cases.
This fixes a regression introduced by 3.5-rc1.

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>