target/ppc: Fix vsum2sws

target/ppc: Fix vsum2sws

A recent cleanup changed the pre zeroing of the result from 64 bit
to 32 bit operations:

-        result.u64[i] = 0;
+        result.VsrW(i) = 0;

This corrupts the result.

Fixes: 60594fea298d ("target/ppc: remove various HOST_WORDS_BIGENDIAN hacks in int_helper.c")
Signed-off-by: Anton Blanchard <anton@ozlabs.org>
Message-Id: <20190507004811.29968-9-anton@ozlabs.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
(upstream commit 7fa0ddc1d63806769d1b6246a62708d3bde39037)
Acked-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>