Fix jit.dump() output for IR_CONV.

src/jit/dump.lua

@@ -272,7 +272,7 @@ local litname = {
     s = irtype[band(shr(mode, 5), 31)].."."..s
     if band(mode, 0x400) ~= 0 then s = s.." trunc"
     elseif band(mode, 0x800) ~= 0 then s = s.." sext" end
-    local c = shr(mode, 14)
+    local c = shr(mode, 12)
     if c == 2 then s = s.." index" elseif c == 3 then s = s.." check" end
     t[mode] = s
     return s