powerpc/64: Fix checksum folding in csum_add()

Paul's patch to fix checksum folding, commit b492f7e ("powerpc/64:
Fix checksum folding in csum_tcpudp_nofold and ip_fast_csum_nofold")
missed a case in csum_add(). Fix it.

Signed-off-by: Shile Zhang <[email protected]>
Acked-by: Paul Mackerras <[email protected]>
Signed-off-by: Michael Ellerman <[email protected]>

Author: Shile Zhang

arch/powerpc/include/asm/checksum.h

@@ -112,7 +112,7 @@ static inline __wsum csum_add(__wsum csum, __wsum addend)
 
 #ifdef __powerpc64__
 	res += (__force u64)addend;
-	return (__force __wsum)((u32)res + (res >> 32));
+	return (__force __wsum) from64to32(res);
 #else
 	asm("addc %0,%0,%1;"
 	    "addze %0,%0;"