habanalabs: use proper max_power variable for device utilization

The max_power variable which is used for calculating the device
utilization is the ASIC specific property which is set during init.
However, the max value can be modified via sysfs, and thus the updated
value in the device structure should be used instead.

Signed-off-by: Tomer Tayar <ttayar@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>