net: qrtr: Start MHI channels during init

Start MHI device channels so that transfers can be performed.
The MHI stack does not auto-start channels anymore.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Acked-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>