drivers/perf: Simplify EVENT ATTR macro in fsl_imx8_ddr_perf.c

Use common macro PMU_EVENT_ATTR_ID to simplify IMX8_DDR_PMU_EVENT_ATTR

Reviewed by Frank Li <Frank .li@nxp.com>

Cc: Frank Li <Frank.li@nxp.com>
Cc: Will Deacon <will@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Qi Liu <liuqi115@huawei.com>
Link: https://lore.kernel.org/r/1623220863-58233-7-git-send-email-liuqi115@huawei.com


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