fpga: dfl-fme-perf.c
Add NULL check in the fme_perf_pmu_register

When devm_kasprintf() fails, it returns a NULL pointer. However, this return value is not properly checked in the function fme_perf_pmu_register. 

A NULL check should be added after the devm_kasprintf call to handle potential NULL pointer dereference error.

CODE:
	pmu->capabilities =	PERF_PMU_CAP_NO_INTERRUPT |
				PERF_PMU_CAP_NO_EXCLUDE;

	name = devm_kasprintf(priv->dev, GFP_KERNEL, "dfl_fme%d", pdev->id);

	ret = perf_pmu_register(pmu, name, -1);
	if (ret)
		return ret;