drivers/perf: fix return value check in ali_drw_pmu_probe()

drivers/perf: fix return value check in ali_drw_pmu_probe()

In case of error, devm_ioremap_resource() returns ERR_PTR(),
and never returns NULL. The NULL test in the return value
check should be replaced with IS_ERR().

Fixes: cf7b61073e45 ("drivers/perf: add DDR Sub-System Driveway PMU driver for Yitian 710 SoC")
Signed-off-by: Sun Ke <sunke32@huawei.com>
Acked-by: Will Deacon <will@kernel.org>
Reviewed-by: Shuai Xue <xueshuai@linux.alibaba.com>
Link: https://lore.kernel.org/r/20220924032127.313156-1-sunke32@huawei.com
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>