ila: Fix uninitialised return value in ila_xlat_nl_cmd_flush

This patch fixes an uninitialised return value error in
ila_xlat_nl_cmd_flush.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: 6c4128f65857 ("rhashtable: Remove obsolete...")
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>