HID: uhid: Fix returning EPOLLOUT from uhid_char_poll

BugLink: https://bugs.launchpad.net/bugs/1859865

commit be54e746 upstream.

Always return EPOLLOUT from uhid_char_poll to allow polling /dev/uhid
for writable state.

Fixes: 1f9dec1e ("HID: uhid: allow poll()'ing on uhid devices")
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
Cc: stable@vger.kernel.org
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Connor Kuehl <connor.kuehl@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>

drivers/hid/uhid.c

@@ -26,6 +26,7 @@
 #include <linux/uhid.h>
 #include <linux/wait.h>
 #include <linux/uaccess.h>
+#include <linux/eventpoll.h>
 
 #define UHID_NAME	"uhid"
 #define UHID_BUFSIZE	32
@@ -774,7 +775,7 @@ static unsigned int uhid_char_poll(struct file *file, poll_table *wait)
 	if (uhid->head != uhid->tail)
 		return POLLIN | POLLRDNORM;
 
-	return 0;
+	return EPOLLOUT | EPOLLWRNORM;
 }
 
 static const struct file_operations uhid_fops = {