media: dvbdev: Initialize sbuf

BugLink: https://bugs.launchpad.net/bugs/2076435

[ Upstream commit 17d1316de0d7dc1bdc5d6e3ad4efd30a9bf1a381 ]

Because the size passed to copy_from_user() cannot be known beforehand,
it needs to be checked during runtime with check_object_size. That makes
gcc believe that the content of sbuf can be used before init.

Fix:
./include/linux/thread_info.h:215:17: warning: ‘sbuf’ may be used uninitialized [-Wmaybe-uninitialized]

Signed-off-by: Ricardo Ribalda <ribalda@chromium.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: Portia Stephens <portia.stephens@canonical.com>
Signed-off-by: Roxana Nicolescu <roxana.nicolescu@canonical.com>

drivers/media/dvb-core/dvbdev.c

@@ -956,7 +956,7 @@ int dvb_usercopy(struct file *file,
 		 int (*func)(struct file *file,
 			     unsigned int cmd, void *arg))
 {
-	char    sbuf[128];
+	char    sbuf[128] = {};
 	void    *mbuf = NULL;
 	void    *parg = NULL;
 	int     err  = -EINVAL;