drivers/message/i2o/i2o_config.c: fix deadlock in compat_ioctl(I2OGETIOPS)

i2o_cfg_compat_ioctl(I2OGETIOPS) locks i2o_cfg_mutex and then calls
i2o_cfg_ioctl(I2OGETIOPS) that locks i2o_cfg_mutex as well.  A deadlock
is guaranteed.

Found by Linux Driver Verification project (linuxtesting.org).
Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/message/i2o/i2o_config.c

@@ -754,19 +754,19 @@ static long i2o_cfg_compat_ioctl(struct file *file, unsigned cmd,
 				 unsigned long arg)
 {
 	int ret;
-	mutex_lock(&i2o_cfg_mutex);
 	switch (cmd) {
 	case I2OGETIOPS:
 		ret = i2o_cfg_ioctl(file, cmd, arg);
 		break;
 	case I2OPASSTHRU32:
+		mutex_lock(&i2o_cfg_mutex);
 		ret = i2o_cfg_passthru32(file, cmd, arg);
+		mutex_unlock(&i2o_cfg_mutex);
 		break;
 	default:
 		ret = -ENOIOCTLCMD;
 		break;
 	}
-	mutex_unlock(&i2o_cfg_mutex);
 	return ret;
 }