Fix horizontal mosaic on sprites (#2084)

The code itself is correct, but the variable being read is the Y mosaic
coordinate, not the X coordinate.

src/GPU2D_Soft.cpp

@@ -1507,7 +1507,7 @@ void SoftRenderer::ApplySpriteMosaicX()
 
     u32* objLine = OBJLine[CurUnit->Num];
 
-    u8* curOBJXMosaicTable = MosaicTable[CurUnit->OBJMosaicSize[1]].data();
+    u8* curOBJXMosaicTable = MosaicTable[CurUnit->OBJMosaicSize[0]].data();
 
     u32 lastcolor = objLine[0];