iscsi: fix leak of session->initiator_alias

session->initiator_alias is not freed in error paths of
session_create() and even in the normal path of session_destroy().

This fixes these leak bugs.

Note that we don't have to do a null check for
session->initiator_alias before calling free(session->initiator_alias)
because free() function simply ignores NULL pointer.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>