Documentation/gpu: remove spurious "+" in amdgpu.rst

Not sure why that was there.  Remove it.
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

Documentation/gpu/amdgpu.rst

@@ -300,8 +300,8 @@ pcie_replay_count
 .. kernel-doc:: drivers/gpu/drm/amd/amdgpu/amdgpu_device.c
    :doc: pcie_replay_count
 
-+GPU SmartShift Information
-============================
+GPU SmartShift Information
+==========================
 
 GPU SmartShift information via sysfs