etnaviv: perfmon: fix total and idle HI cyleces readout

[ Upstream commit 15ff4a7b584163b12b118a2c381529f05ff3a94d ]

As seen at CodeAurora's linux-imx git repo in imx_4.19.35_1.0.0 branch.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>