xen: pcpu: remove unnecessary __ref annotation

The __ref annotation has been there since many years now, but the
reason why it has been added has been removed from the code long ago.

[jgross: clarify commit message]

Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Cc: xen-devel@lists.xenproject.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Sergio Miguéns Iglesias <sergio@lony.xyz>
Reviewed-by: Juergen Gross <jgross@suse.com>
Message-ID: <20241202085910.5539-1-sergio@lony.xyz>
Signed-off-by: Juergen Gross <jgross@suse.com>

drivers/xen/pcpu.c

@@ -105,7 +105,7 @@ static ssize_t online_show(struct device *dev,
 	return sprintf(buf, "%u\n", !!(cpu->flags & XEN_PCPU_FLAGS_ONLINE));
 }
 
-static ssize_t __ref online_store(struct device *dev,
+static ssize_t online_store(struct device *dev,
 				  struct device_attribute *attr,
 				  const char *buf, size_t count)
 {