cifs: Fix an uninitialised variable

Fix an uninitialised variable introduced in cifs.

Fixes: 3d78fe73 ("cifs: Build the RDMA SGE list directly from an iterator")
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Paulo Alcantara (SUSE) <pc@cjr.nz>
cc: Steve French <sfrench@samba.org>
cc: Shyam Prasad N <nspmangalore@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Tom Talpey <tom@talpey.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-rdma@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>