x86: ioremap fix failing nesting check

Mika Kukkonen noticed that the nesting check in early_iounmap() is not
actually done.

Reported-by: Mika Kukkonen <mikukkon@srv1-m700-lanp.koti>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Cc: torvalds@linux-foundation.org
Cc: arjan@linux.intel.com
Cc: mikukkon@iki.fi
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>