x86, mm: fix misuse of debug_kmap_atomic

Impact: fix CONFIG_DEBUG_HIGHMEM=y breakage

Commit 7ca43e75 ("mm: use debug_kmap_atomic") introduced some
debug_kmap_atomic() calls in the wrong places.

Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
LKML-Reference: <20090402070126.GA3951@localhost.localdomain>
Signed-off-by: Ingo Molnar <mingo@elte.hu>