Fix incorrect integer cast in predux<half2>().

Bug corrupts results on Maxwell and earlier GPU architectures.

Eigen/src/Core/arch/CUDA/PacketMathHalf.h

diff --git a/Eigen/src/Core/arch/CUDA/PacketMathHalf.h b/Eigen/src/Core/arch/CUDA/PacketMathHalf.h
index ce48e4b..e3e45b0 100644
--- a/Eigen/src/Core/arch/CUDA/PacketMathHalf.h
+++ b/Eigen/src/Core/arch/CUDA/PacketMathHalf.h
@@ -231,7 +231,7 @@
 #else
   float a1 = __low2float(a);
   float a2 = __high2float(a);
-  return Eigen::half(half_impl::raw_uint16_to_half(__float2half_rn(a1 + a2)));
+  return Eigen::half(__float2half_rn(a1 + a2));
 #endif
 }
 
@@ -265,7 +265,7 @@
 #else
   float a1 = __low2float(a);
   float a2 = __high2float(a);
-  return Eigen::half(half_impl::raw_uint16_to_half(__float2half_rn(a1 * a2)));
+  return Eigen::half(__float2half_rn(a1 * a2));
 #endif
 }