sysfs: Unbreak the build around sysfs_bin_attr_simple_read()

Günter reports build breakage for m68k "m5208evb_defconfig" plus
CONFIG_BLK_DEV_INITRD=y caused by commit 66bc1a1 ("treewide:
Use sysfs_bin_attr_simple_read() helper").

The defconfig disables CONFIG_SYSFS, so sysfs_bin_attr_simple_read()
is not compiled into the kernel.  But init/initramfs.c references
that function in the initializer of a struct bin_attribute.

Add an empty static inline to avoid the build breakage.

Fixes: 66bc1a1 ("treewide: Use sysfs_bin_attr_simple_read() helper")
Reported-by: Guenter Roeck <linux@roeck-us.net>
Closes: https://lore.kernel.org/r/e12b0027-b199-4de7-b83d-668171447ccc@roeck-us.net
Signed-off-by: Lukas Wunner <lukas@wunner.de>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Rafael J. Wysocki <rafael@kernel.org>
Link: https://lore.kernel.org/r/05f4290439a58730738a15b0c99cd8576c4aa0d9.1716461752.git.lukas@wunner.de
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: l1k

include/linux/sysfs.h

@@ -750,6 +750,15 @@ static inline int sysfs_emit_at(char *buf, int at, const char *fmt, ...)
 {
 	return 0;
 }
+
+static inline ssize_t sysfs_bin_attr_simple_read(struct file *file,
+						 struct kobject *kobj,
+						 struct bin_attribute *attr,
+						 char *buf, loff_t off,
+						 size_t count)
+{
+	return 0;
+}
 #endif /* CONFIG_SYSFS */
 
 static inline int __must_check sysfs_create_file(struct kobject *kobj,