kernel: misc: heartbeat: fix invalid CAN instance.

when MCU is down, qti driver will fail to probe the CAN port,
and heartbeat will not have valid instance to transact with CAN,
hence it will exit with probe failure reason.


Change-Id: I59f35a09e9507d79dc2edc35644d10c73d922f2f
Signed-off-by: Vivek Mano Chandar <quic_vchandar@quicinc.com>
Signed-off-by: Hari Krishnamachari Kammari <quic_kammarih@quicinc.com>