[Bug]: Unexpected Brightness Increase When Setting Contrast via Intel VPP

### Which component impacted?

Video Processing

### Is it regression? Good in old configuration?

Yes, it's good in old version

### What happened?

I'm encountering an issue with Intel's Video Processing Pipeline (VPP) while applying the Contrast effect. When I set the contrast to a high value (e.g., 10.0f), while keeping all other effects to their default values, the resulting output unexpectedly appears brighter as well, even though Brightness was not modified.

Platform: Windows
GPU Chip: Iris(R) Xe Graphics

Code Snippet:

mfxExtVPPProcAmp input = {};
input.Header.BufferId = MFX_EXTBUFF_VPP_PROCAMP;
input.Header.BufferSz = sizeof(mfxExtVPPProcAmp);

// Only contrast changed, other values at default
input.Brightness = 0.0f;
input.Contrast = 10.0f;
input.Hue = 0.0f;
input.Saturation = 1.0f;

Expected Behavior:
Only contrast should be adjusted in the output frame, with no noticeable change in brightness.

Actual Behavior:
The output appears not only higher in contrast but also unintentionally brighter, suggesting either:
An internal coupling between contrast and brightness in the VPP implementation.
A possible bug in how the contrast value is processed or clamped.

Activity

### What's the usage scenario when you are seeing the problem?

Transcode for media delivery

### What impacted?

_No response_

### Debug Information

_No response_

### Do you want to contribute a patch to fix the issue?

None