deadline_test: Increase buffer to avoid overflow

Increase the size of the char buffer. gcc 9.1.1 reports:

src/sched_deadline/deadline_test.c:1803:24: warning: ‘%d’ directive writing between 1 and 11 bytes into a region of size 10 [-Wformat-overflow=]
 1803 |   sprintf(setcpu_buf, "%d", cpu_count - 1);
      |                        ^~
src/sched_deadline/deadline_test.c:1803:23: note: directive argument in the range [-2147483648, 2147483646]
 1803 |   sprintf(setcpu_buf, "%d", cpu_count - 1);
      |                       ^~~~
src/sched_deadline/deadline_test.c:1803:3: note: ‘sprintf’ output between 2 and 12 bytes into a destination of size 10
 1803 |   sprintf(setcpu_buf, "%d", cpu_count - 1);
      |   ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: John Kacur <jkacur@redhat.com>

src/sched_deadline/deadline_test.c

@@ -1795,7 +1795,7 @@ int main (int argc, char **argv)
 
 	/* -b has us bind to the last CPU. */
 	if (!all_cpus && !setcpu) {
-		setcpu_buf = malloc(10);
+		setcpu_buf = malloc(12);
 		if (!setcpu_buf) {
 			perror("malloc");
 			exit(-1);