net: can: c_can: Fix DCAN2 stuck in transition

Done bit was never initialized for DCAN2 and so was left as 0.
Fix this up.

This fixes the DCAN2 instance being stuck in transition
when DCAN2 module is disabled even when not connected to CAN
traffic.

Now it correctly transitions to "disabled/can't be accessed"
and we no longer see "omap_hwmod: dcan2: _wait_target_disable failed"
messages in kernel log.

Signed-off-by: Roger Quadros <rogerq@ti.com>