smb: client: remove pointless sc->recv_io.credits.count rollback

smb: client: remove pointless sc->recv_io.credits.count rollback

We either reach this code path before we call
new_credits = manage_credits_prior_sending(sc),
which means new_credits is still 0
or the connection is already broken as
smbd_post_send() already called
smbd_disconnect_rdma_connection().

This will also simplify further changes.

Cc: <stable@vger.kernel.org> # 6.18.x
Cc: Steve French <smfrench@gmail.com>
Cc: Tom Talpey <tom@talpey.com>
Cc: Long Li <longli@microsoft.com>
Cc: Namjae Jeon <linkinjeon@kernel.org>
Cc: linux-cifs@vger.kernel.org
Cc: samba-technical@lists.samba.org
Signed-off-by: Stefan Metzmacher <metze@samba.org>
Signed-off-by: Steve French <stfrench@microsoft.com>