[S390] dasd: fix use after free in dbf

Writing to /proc/dasd/statistics while the debug level of the
generic dasd debug entry is set to DBF_DEBUG will lead to an
use after free when accessing the debug entry later.
Since for the format string "%s" in the s390 dbf only a pointer
to the string is stored in the debug feature and the buffer used
here is freed afterwards.

To fix this just remove the debug message.
Signed-off-by: NSebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: NMartin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/block/dasd_proc.c

@@ -251,7 +251,6 @@ static ssize_t dasd_stats_proc_write(struct file *file,
 	buffer = dasd_get_user_string(user_buf, user_len);
 	if (IS_ERR(buffer))
 		return PTR_ERR(buffer);
-	DBF_EVENT(DBF_DEBUG, "/proc/dasd/statictics: '%s'\n", buffer);
 
 	/* check for valid verbs */
 	str = skip_spaces(buffer);