staging: most: move initialization of pointer

This patch makes function store_add_link initialize the pointer to an AIM
right before the channel is probed. It is needed, the AIM may already call
most_start_channel while probe_channel is still running. At this point the
pointer to the AIM must not be NULL.

Signed-off-by: Christian Gromm <christian.gromm@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>