drm/amd/display: Fix disable_otg_wa logic

drm/amd/display: Fix disable_otg_wa logic

[Why]
When switching to another HDMI mode, we are unnecesarilly
disabling/enabling FIFO causing both HPO and DIG registers to be set at
the same time when only HPO is supposed to be set.

This can lead to a system hang the next time we change refresh rates as
there are cases when we don't disable OTG/FIFO but FIFO is enabled when
it isn't supposed to be.

[How]
Removing the enable/disable FIFO entirely.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Nicholas Susanto <nicholas.susanto@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>