staging: vc04_services: vchiq_arm: Fix initialisation check

The vchiq_state used to be obtained through an accessor
which would validate that the VCHIQ had been initialised
correctly with the remote.

In commit 42a2f666 ("staging: vc04_services: Move global g_state to
vchiq_state") the global state was moved to the vchiq_mgnt structures
stored as a vchiq instance specific context. This conversion removed the
helpers and instead replaced users of this helper with the assumption
that the state is always available and the remote connected.

Fix this broken assumption by re-introducing the logic that was lost
during the conversion.

Fixes: 42a2f666

 ("staging: vc04_services: Move global g_state to vchiq_state")
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>