mhi: core: auto-start uplink channel before client driver probe

For auto-start feature, MHI client can queue data uplink as soon
as the probe is received. If that is attempted, there is a
chance of NULL pointer access as channel may not be initialized.
Change the order to allow initializing the uplink channel before
probe is called.

CRs-Fixed: 2501803
Change-Id: I90b65bd9a015534d38ba0e4e931d3a2b13bcbf18
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Chris Lew <clew@codeaurora.org>