net/smc: put sk reference if close work was canceled

Note that we always hold a reference to sock when attempting
to submit close_work. Therefore, if we have successfully
canceled close_work from pending, we MUST release that reference
to avoid potential leaks.

Fixes: 42bfba9e ("net/smc: immediate termination for SMCD link groups")
Signed-off-by: D. Wythe <alibuda@linux.alibaba.com>
Reviewed-by: Dust Li <dust.li@linux.alibaba.com>
Signed-off-by: David S. Miller <davem@davemloft.net>