cifs: Fix cifs_limit_bvec_subset() to correctly check the maxmimum size

Fix cifs_limit_bvec_subset() so that it limits the span to the maximum
specified and won't return with a size greater than max_size.

Fixes: d08089f6 ("cifs: Change the I/O paths to use an iterator rather than a page list")
Cc: stable@vger.kernel.org # 6.3
Reported-by: Shyam Prasad N <sprasad@microsoft.com>
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: Steve French <smfrench@gmail.com>
cc: Rohith Surabattula <rohiths.msft@gmail.com>
cc: Paulo Alcantara <pc@manguebit.com>
cc: Tom Talpey <tom@talpey.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>