smb3: fix lock ordering potential deadlock in cifs_sync_mid_result

Coverity spotted that the cifs_sync_mid_result function could deadlock

"Thread deadlock (ORDER_REVERSAL) lock_order: Calling spin_lock acquires
lock TCP_Server_Info.srv_lock while holding lock TCP_Server_Info.mid_lock"

Addresses-Coverity: 1590401 ("Thread deadlock (ORDER_REVERSAL)")
Cc: stable@vger.kernel.org
Reviewed-by: Shyam Prasad N <sprasad@microsoft.com>
Signed-off-by: Steve French <stfrench@microsoft.com>