fix lguest rmmod "bad pgd"

After 17d57a92 ("x86: fix x86-32 early
fixmap initialization.") removing lg.ko caused a printk from vunmap:

	mm/memory.c:115: bad pgd 004b3027.

On the second use after module load, the kernel crashes.

This fixes the immediate problem (accessed and dirty bits not set as
expected in pmd_none_or_clear_bad).  I can't see why this would cause
a crash, but I haven't been able to reproduce it once this is applied.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

arch/x86/kernel/head_32.S

@@ -196,7 +196,7 @@ default_entry:
 	/* Do an early initialization of the fixmap area */
 	movl $(swapper_pg_dir - __PAGE_OFFSET), %edx
 	movl $(swapper_pg_pmd - __PAGE_OFFSET), %eax
-	addl $0x007, %eax			/* 0x007 = PRESENT+RW+USER */
+	addl $0x67, %eax			/* 0x67 == _PAGE_TABLE */
 	movl %eax, 4092(%edx)
 
 	xorl %ebx,%ebx				/* This is the boot CPU (BSP) */