x86/mcheck: Explicit cleanup on failure in mce_amd

If the ONLINE callback fails, the driver does not any clean up right
away instead it waits to get to the DEAD stage to do it. Yes, it waits.
Since we don't pass the error code back to the caller, no one knows.

Do the clean up right away so it does not look like a leak.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Tony Luck <tony.luck@intel.com>
Cc: rt@linutronix.de
Cc: linux-edac@vger.kernel.org
Link: http://lkml.kernel.org/r/20161110174447.11848-3-bigeasy@linutronix.deSigned-off-by: Thomas Gleixner <tglx@linutronix.de>

arch/x86/kernel/cpu/mcheck/mce_amd.c

@@ -1087,6 +1087,7 @@ static void threshold_remove_device(unsigned int cpu)
 		threshold_remove_bank(cpu, bank);
 	}
 	kfree(per_cpu(threshold_banks, cpu));
+	per_cpu(threshold_banks, cpu) = NULL;
 }
 
 /* create dir/files for all valid threshold banks */
@@ -1108,9 +1109,11 @@ static int threshold_create_device(unsigned int cpu)
 			continue;
 		err = threshold_create_bank(cpu, bank);
 		if (err)
-			return err;
+			goto err;
 	}
-
+	return err;
+err:
+	threshold_remove_device(cpu);
 	return err;
 }