fix dnetc overflow issue.
fix dnetc overflow issue.

the overflow type should be unsigned for uadd_with_overflow.
this patch fixed the "dnetc -test rc5-72 0" 15 fails out of
32 when disabled bswap.

Signed-off-by: Luo Xionghu <c3dafbeb50547b880155fb36e6f40d38b44f6611@intel.com>
Reviewed-by: Zhigang Gong <e04a7b9b70b1e4c6318cf117dcd1a9056e14b97a@intel.com>

wdv4758h/beignet,wdv4758h/beignet,zhenyw/beignet,zhenyw/beignet,wdv4758h/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,freedesktop-unofficial-mirror/beignet,zhenyw/beignet,wdv4758h/beignet,zhenyw/beignet,freedesktop-unofficial-mirror/beignet,wdv4758h/beignet