slirp: fix unused return value, spotted by clang

Fix clang errors like:
  CC    slirp/cksum.o
/src/qemu/slirp/cksum.c:78:3: error: expression result unused [-Wunused-value]
                REDUCE;
/src/qemu/slirp/cksum.c:45:66: note: instantiated from:

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/cksum.c b/cksum.c
index e5f8c11..c50cfea 100644
--- a/cksum.c
+++ b/cksum.c
@@ -46,7 +46,7 @@
     {                                    \
         l_util.l = sum;                  \
         sum = l_util.s[0] + l_util.s[1]; \
-        ADDCARRY(sum);                   \
+        (void)ADDCARRY(sum);             \
     }
 
 int cksum(struct mbuf *m, int len)