GS/HW: Make sure it's not a channel shuffle when the alpha of a targe…

…t is used as source.

The alpha of a target used a source is meaningless to us,
since it's not really an indexed texture.

pcsx2/GS/Renderers/HW/GSRendererHW.cpp

@@ -2576,7 +2576,9 @@ void GSRendererHW::Draw()
 			// We don't know the alpha range of direct sources when we first tried to optimize the alpha test.
 			// Moving the texture lookup before the ATST optimization complicates things a lot, so instead,
 			// recompute it, and everything derived from it again if it changes.
-			if (src->m_valid_alpha_minmax)
+			// No channel shuffle as the alpha of a target used a source is meaningless to us,
+			// since it's not really an indexed texture.
+			if (!IsPossibleChannelShuffle() && src->m_valid_alpha_minmax)
 			{
 				CalcAlphaMinMax(src->m_alpha_minmax.first, src->m_alpha_minmax.second);