drm/amd/display: Remove wrong signal from vrr calculation

drm/amd/display: Remove wrong signal from vrr calculation

In some of the merge conflict fixes, one '+' was accidentally left at
the beginning of the line. Fortunately, this did not cause any major
issues since it acted as a number signal. This commit addresses this
issue by removing the extra '+'.

Acked-by: Wayne Lin <wayne.lin@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>