wil6210: update the disconnect sequence for the IPA disconnect

In the disconnect flow, descriptor ring being freed before the
IPA pipe being disabled.
disable/disconnect the IPA pipe before freeing the descriptor ring.

Change-Id: I4c953306660e0bd2d60585d0f84d8a7ed63c821e
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>