smc: cleanup close checking during data receival

When waiting for data to be received it must be checked if the
peer signals shutdown. The SMC code uses two different checks
for this purpose, even though just one check is sufficient.
This patch removes the superfluous test for SOCK_DONE.

Signed-off-by: Ursula Braun <ubraun@linux.vnet.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>