msm: mhi_dev: Initialize UCI client channel numbers early

Move the channel number initialization for UCI clients to
uci_init_client_attributes function to ensure the correct channel
number is used for registering callback with the MHI driver.
Correct the index used to retrieve the client handle.

Change-Id: I5987366aed582ac47895a1310e0e0ee0de07c470
Signed-off-by: Siva Kumar Akkireddi <sivaa@codeaurora.org>