powercap: intel_rapl: Change an error pointer to NULL

powercap: intel_rapl: Change an error pointer to NULL

The rapl_find_package_domain_cpuslocked() function is supposed to
return NULL on error.

This new error patch returns ERR_PTR(-EINVAL) but none of the callers
check for that so it would lead to an Oops.

Fixes: 26096aed255f ("powercap/intel_rapl: Fix the energy-pkg event for AMD CPUs")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://patch.msgid.link/fa719c6a-8d3b-4cca-9b43-bcd477ff6655@stanley.mountain
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>