mm_types.h: change set_page_private to inline function

Change it to inline function to make callers use the proper argument.  And
no need for it to be macro per Andrew's comment [1].

[1] https://lore.kernel.org/lkml/20200518221235.1fa32c38e5766113f78e3f0d@linux-foundation.org/Signed-off-by: Guoqing Jiang <guoqing.jiang@cloud.ionos.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Link: http://lkml.kernel.org/r/20200525203149.18802-1-guoqing.jiang@cloud.ionos.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm_types.h

@@ -240,7 +240,11 @@ static inline atomic_t *compound_pincount_ptr(struct page *page)
 #define PAGE_FRAG_CACHE_MAX_ORDER	get_order(PAGE_FRAG_CACHE_MAX_SIZE)
 
 #define page_private(page)		((page)->private)
-#define set_page_private(page, v)	((page)->private = (v))
+
+static inline void set_page_private(struct page *page, unsigned long private)
+{
+	page->private = private;
+}
 
 struct page_frag_cache {
 	void * va;