mm/page_alloc: remove unnecessary __maybe_unused in order_to_pindex()

The `movable` variable is always used when `CONFIG_TRANSPARENT_HUGEPAGE`
is enabled, so the `__maybe_unused` attribute is not necessary.  This
patch removes it and keeps the variable declaration within the `#ifdef`
block for better clarity.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Liu Ye<[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: Liu Ye

mm/page_alloc.c

@@ -509,9 +509,9 @@ static void bad_page(struct page *page, const char *reason)
 
 static inline unsigned int order_to_pindex(int migratetype, int order)
 {
-	bool __maybe_unused movable;
 
 #ifdef CONFIG_TRANSPARENT_HUGEPAGE
+	bool movable;
 	if (order > PAGE_ALLOC_COSTLY_ORDER) {
 		VM_BUG_ON(order != HPAGE_PMD_ORDER);