SUNRPC: remove an unnecessary if statement

If req allocated failed just goto out_free, no need to check the
'i < num_prealloc'. There is just code simplification, no
functional changes.

Signed-off-by: Wang Weidong <wangweidong1@huawei.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>