x86, mm: remove unnecessary include file from iomap_32.c

asm/highmem.h inclusion is added to use kmap_atomic_prot_pfn()
by commit bb6d59ca

Now kmap_atomic_prot_pfn is moved to iomap_32.c
by commit dd63fdcc

So the asm/highmem.h inclusion in iomap_32.c is unnecessary now.
Signed-off-by: NAkinobu Mita <akinobu.mita@gmail.com>
LKML-Reference: <20090315151517.GA29074@localhost.localdomain>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/mm/iomap_32.c

@@ -18,7 +18,6 @@
 
 #include <asm/iomap.h>
 #include <asm/pat.h>
-#include <asm/highmem.h>
 #include <linux/module.h>
 
 int is_io_mapping_possible(resource_size_t base, unsigned long size)