cifs: open_cached_dir should not rely on primary channel

cifs: open_cached_dir should not rely on primary channel

[ Upstream commit 936eba9cfb5cfbf6a2c762cd163605f2b784e03e ]

open_cached_dir today selects ses->server a.k.a primary channel
to send requests. When multichannel is used, the primary
channel maybe down. So it does not make sense to rely only
on that channel.

This fix makes this function pick a channel with the standard
helper function cifs_pick_channel.

Signed-off-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>