ARM: thp: fix unterminated ifdef in header file

ARM: thp: fix unterminated ifdef in header file

A recent change accidentally removed one line more than it should
have, causing the build to fail with ARM LPAE:

In file included from /git/arm-soc/arch/arm/include/asm/pgtable.h:31:0,
                 from /git/arm-soc/include/linux/mm.h:55,
                 from /git/arm-soc/arch/arm/kernel/asm-offsets.c:15:
/git/arm-soc/arch/arm/include/asm/pgtable-3level.h:20:0: error: unterminated #ifndef
 #ifndef _ASM_PGTABLE_3LEVEL_H

This puts the line back where it was.

Fixes: f054144a1b23 ("arm, thp: remove infrastructure for handling splitting PMDs")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>