drm/radeon: adjust pll when audio is not enabled

Fixes display problems with some monitors when audio
is not enabled.

Bugs:
https://bugs.freedesktop.org/show_bug.cgi?id=89505
https://bugzilla.kernel.org/show_bug.cgi?id=94171


Plus several reports on IRC.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org