msm: vidc: Add instance to instance list prior to CORE_INIT

During CORE_INIT, driver votes for bus only if core->instances list
is not empty. Since the current video instance is added to core->instances
list after core init, driver fails to vote for bus. This causes ion_map to
hang and resets the device.

Change-Id: Ia68a953572852db63737f30998cf10c5db151292
Signed-off-by: Srinu Gorle <sgorle@codeaurora.org>