[SCSI] scsi_debug: fix invalid value check for guard module parameter

In the module initialization, invalid value for guard module parameter
is detected by the following check:

        if (scsi_debug_guard > 1) {
                printk(KERN_ERR "scsi_debug_init: guard must be 0 or 1\n");
                return -EINVAL;
        }

But this check isn't enough, because the type of scsi_debug_guard is
'int' and scsi_debug_guard could be a negative value.

This fixes it by changing the type of scsi_debug_guard to 'unsigned int'
instead of adding extra check for a negative value.

Reported-by: Joe Perches <joe@perches.com>
Signed-off-by: Akinobu Mita <akinobu.mita@gmail.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

drivers/scsi/scsi_debug.c

@@ -169,7 +169,7 @@ static int scsi_debug_dix = DEF_DIX;
 static int scsi_debug_dsense = DEF_D_SENSE;
 static int scsi_debug_every_nth = DEF_EVERY_NTH;
 static int scsi_debug_fake_rw = DEF_FAKE_RW;
-static int scsi_debug_guard = DEF_GUARD;
+static unsigned int scsi_debug_guard = DEF_GUARD;
 static int scsi_debug_lowest_aligned = DEF_LOWEST_ALIGNED;
 static int scsi_debug_max_luns = DEF_MAX_LUNS;
 static int scsi_debug_max_queue = SCSI_DEBUG_CANQUEUE;
@@ -2754,7 +2754,7 @@ module_param_named(dix, scsi_debug_dix, int, S_IRUGO);
 module_param_named(dsense, scsi_debug_dsense, int, S_IRUGO | S_IWUSR);
 module_param_named(every_nth, scsi_debug_every_nth, int, S_IRUGO | S_IWUSR);
 module_param_named(fake_rw, scsi_debug_fake_rw, int, S_IRUGO | S_IWUSR);
-module_param_named(guard, scsi_debug_guard, int, S_IRUGO);
+module_param_named(guard, scsi_debug_guard, uint, S_IRUGO);
 module_param_named(lbpu, scsi_debug_lbpu, int, S_IRUGO);
 module_param_named(lbpws, scsi_debug_lbpws, int, S_IRUGO);
 module_param_named(lbpws10, scsi_debug_lbpws10, int, S_IRUGO);
@@ -3184,7 +3184,7 @@ DRIVER_ATTR(dif, S_IRUGO, sdebug_dif_show, NULL);
 
 static ssize_t sdebug_guard_show(struct device_driver *ddp, char *buf)
 {
-	return scnprintf(buf, PAGE_SIZE, "%d\n", scsi_debug_guard);
+	return scnprintf(buf, PAGE_SIZE, "%u\n", scsi_debug_guard);
 }
 DRIVER_ATTR(guard, S_IRUGO, sdebug_guard_show, NULL);