Fixed warning in luminance pyramid pass when FP16 is enabled

Assets/Resources/FSR3/shaders/fsr3upscaler/spd/ffx_spd.h

@@ -735,7 +735,7 @@ void SpdDownsampleMips_0_1_LDSH(FfxUInt32 x, FfxUInt32 y, FfxUInt32x2 workGroupI
     if (mips <= 1)
         return;
 
-    for (FfxInt32 i = 0; i < 4; i++)
+    for (FfxUInt32 i = 0; i < 4; i++)
     {
         SpdStoreIntermediateH(x, y, v[i]);
         ffxSpdWorkgroupShuffleBarrier();