drivers/perf: fsl_imx8_ddr_perf: Remove set-but-not-used variable

active_events is set but not used, remove it.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Link: https://lore.kernel.org/r/20230203121509.3580245-1-s.hauer@pengutronix.de


Signed-off-by: Will Deacon <will@kernel.org>