platform/x86: pmt: Fix a potential Oops on error in probe

mainline inclusion
from mainline-v5.11-rc1
commit d3d73d25
category: feature
bugzilla: https://gitee.com/openeuler/intel-kernel/issues/I596K9


CVE: NA

Intel-SIG: commit d3d73d25 platform/x86: pmt: Fix a potential Oops
on error in probe.
Backport for intel PMT (Platform Monitoring Technology) support

--------------------------------

The "ns->attr_grp" pointer can be NULL so this error handling code needs
to check for that to avoid an Oops.

Fixes: e2729113 ("platform/x86: Intel PMT class driver")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20201117072251.GC1111239@mwanda


Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: yingbao jia <yingbao.jia@intel.com>
Signed-off-by: Jun Tian <jun.j.tian@intel.com>