libct/intelrdt: fix potential nil dereference

In case getIntelRdtData() returns an error, d is set to nil.

In case the error returned is of NotFoundError type (which happens
if resctlr mount is not found in /proc/self/mountinfo), the function
proceeds to call d.join(), resulting in a nil deref and a panic.

In practice, this never happens in runc because of the checks in
intelrdt() function in libcontainer/configs/validate, which raises
an error in case any of the parameters are set in config but
the IntelRTD itself is not available (that includes checking
that the mount point is there).

Nevertheless, the code is wrong, and can result in nil dereference
if some external users uses Apply on a system without resctrl mount.

Fix this by removing the exclusion.

Signed-off-by: Kir Kolyshkin <kolyshkin@gmail.com>

libcontainer/intelrdt/intelrdt.go

@@ -547,7 +547,7 @@ func (m *intelRdtManager) Apply(pid int) (err error) {
 		return nil
 	}
 	d, err := getIntelRdtData(m.config, pid)
-	if err != nil && !IsNotFound(err) {
+	if err != nil {
 		return err
 	}