sctp: cleanup: remove duplicate assignment

This assignment isn't needed because we did it earlier already.

Also another reason to delete the assignment is because it triggers a
Smatch warning about checking for NULL pointers after a dereference.

Reported-by: Vlad Yasevich <vladislav.yasevich@hp.com>
Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Vlad Yasevich <vladislav.yasevich@hp.com>