drm/amd/display: fix condition for setting timing_adjust_pending

timing_adjust_pending is used to defer certain programming sequences
when OTG timing is about to be changed, like with VRR. Insufficient
checking for timing change in this case caused a regression which
reduces PSR Replay residency.

Reviewed-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Robin Chen <robin.chen@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>