smbdirect: Fix error cleanup in smbdirect_map_sges_from_iter()

smbdirect: Fix error cleanup in smbdirect_map_sges_from_iter()

Fix smbdirect_map_sges_from_iter() to use pre-decrement, not post-decrement
so that it cleans up the correct slots.

Fixes: e5fbdde43017 ("cifs: Add a function to build an RDMA SGE list from an iterator")
Closes: https://sashiko.dev/#/patchset/20260326104544.509518-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Reviewed-by: Stefan Metzmacher <metze@samba.org>
cc: Paulo Alcantara <pc@manguebit.org>
cc: Tom Talpey <tom@talpey.com>
cc: linux-cifs@vger.kernel.org
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Steve French <stfrench@microsoft.com>