VSOCK: fix returnvar.cocci warnings

Remove unneeded variable used to store return value.

Generated by: scripts/coccinelle/misc/returnvar.cocci

CC: Asias He <asias@redhat.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Julia Lawall <julia.lawall@lip6.fr>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>