smb: client: Use min() macro

[ Upstream commit 25e68c37 ]

Use the min() macro to simplify the function and improve
its readability.

Signed-off-by: Shen Lichuan <shenlichuan@vivo.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Stable-dep-of: 5349ae5e ("smb: client: let send_done() cleanup before calling smbd_disconnect_rdma_connection()")
Signed-off-by: Sasha Levin <sashal@kernel.org>