thp: move shmem_huge_enabled() outside of SYSFS ifdef

The newly introduced shmem_huge_enabled() function has two definitions,
but neither of them is visible if CONFIG_SYSFS is disabled, leading to a
build error:

  mm/khugepaged.o: In function `khugepaged':
  khugepaged.c:(.text.khugepaged+0x3ca): undefined reference to `shmem_huge_enabled'

This changes the #ifdef guards around the definition to match those that
are used in the header file.

Fixes: e496cf3d7821 ("thp: introduce CONFIG_TRANSPARENT_HUGE_PAGECACHE")
Link: http://lkml.kernel.org/r/20160809123638.1357593-1-arnd@arndb.de
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/shmem.c

@@ -3975,7 +3975,9 @@ static ssize_t shmem_enabled_store(struct kobject *kobj,
 
 struct kobj_attribute shmem_enabled_attr =
 	__ATTR(shmem_enabled, 0644, shmem_enabled_show, shmem_enabled_store);
+#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE && CONFIG_SYSFS */
 
+#ifdef CONFIG_TRANSPARENT_HUGE_PAGECACHE
 bool shmem_huge_enabled(struct vm_area_struct *vma)
 {
 	struct inode *inode = file_inode(vma->vm_file);
@@ -4006,7 +4008,7 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
 			return false;
 	}
 }
-#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE && CONFIG_SYSFS */
+#endif /* CONFIG_TRANSPARENT_HUGE_PAGECACHE */
 
 #else /* !CONFIG_SHMEM */