mhi: Fix double dma free

mhi_deinit_chan_ctxt functionthat takes care of unitializing channel
resources, including unmapping coherent MHI areas, can be called
from different path in case of controller unregistering/removal:
 - From a client driver remove callback, via mhi_unprepare_channel
 - From mhi_driver_remove that unitialize all channels

mhi_driver_remove()
|-> driver->remove()
|    |-> mhi_unprepare_channel()
|        |-> mhi_deinit_chan_ctxt()
|...
|-> mhi_deinit_chan_ctxt()

This leads to double dma freeing...

Fix that by preventing deinit for already uninitialized channel.

Fixes: a7f422f2 ("bus: mhi: Fix channel close issue on driver remove")
Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reported-by: Kalle Valo <kvalo@codeaurora.org>
Tested-by: Kalle Valo <kvalo@codeaurora.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/1612894264-15956-1-git-send-email-loic.poulain@linaro.org


Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>