x86, iomap: Fix wrong page aligned size calculation in ioremapping code

x86 early_iounmap(): fix off-by-one error in page alignment of allocation
size for sizes where size%PAGE_SIZE==1.

Signed-off-by: Florian Zumbiehl <florz@florz.de>
LKML-Reference: <201007202219.o6KMJlES021058@imap1.linux-foundation.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>