GenWQE: Ensure rc is not returning an uninitialized value

rc is not initialized, so genwqe_finish_queue() either returns -EIO or
garbage.  Fortunately the return is not being checked by any callers,
so this has not yet caused any problems. Even so, it makes sense to
fix this small bug in case is is checked in future.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Frank Haverkamp <haver@linux.vnet.ibm.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>