habanalabs: fix backward compatibility of idle check

[ Upstream commit f8abaf37

 ]

Need to take the lower 32 bits of the driver's 64-bit idle mask and put
it in the legacy 32-bit variable that the userspace reads to know the
idle mask.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>