mm:backing-dev: use sysfs_emit in macro defining functions

The cocci script used in commit bdacbb8d04f ("mm: Use sysfs_emit for
struct kobject * uses") does not convert the name##_show macro because the
macro uses concatenation via ##.

Convert it by hand.

Link: https://lkml.kernel.org/r/45ec6cfc177d743f9c0ebaf35e43969dce43af42.1605376435.git.joe@perches.comSigned-off-by: Joe Perches <joe@perches.com>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/backing-dev.c

@@ -150,11 +150,11 @@ static ssize_t read_ahead_kb_store(struct device *dev,
 
 #define BDI_SHOW(name, expr)						\
 static ssize_t name##_show(struct device *dev,				\
-			   struct device_attribute *attr, char *page)	\
+			   struct device_attribute *attr, char *buf)	\
 {									\
 	struct backing_dev_info *bdi = dev_get_drvdata(dev);		\
 									\
-	return snprintf(page, PAGE_SIZE-1, "%lld\n", (long long)expr);	\
+	return sysfs_emit(buf, "%lld\n", (long long)expr);		\
 }									\
 static DEVICE_ATTR_RW(name);
 
@@ -200,11 +200,11 @@ BDI_SHOW(max_ratio, bdi->max_ratio)
 
 static ssize_t stable_pages_required_show(struct device *dev,
 					  struct device_attribute *attr,
-					  char *page)
+					  char *buf)
 {
 	dev_warn_once(dev,
 		"the stable_pages_required attribute has been removed. Use the stable_writes queue attribute instead.\n");
-	return snprintf(page, PAGE_SIZE-1, "%d\n", 0);
+	return sysfs_emit(buf, "%d\n", 0);
 }
 static DEVICE_ATTR_RO(stable_pages_required);