scsi: target: tcmu: fix error resetting qfull_time_out to default

Problem:

$ cat /sys/kernel/config/target/core/user_0/block/attrib/qfull_time_out
-1

$ echo "-1" > /sys/kernel/config/target/core/user_0/block/attrib/qfull_time_out
-bash: echo: write error: Invalid argument

Fix:

This patch will help reset qfull_time_out to its default
i.e. qfull_time_out=-1.
Signed-off-by: Prasanna Kumar Kalever <prasanna.kalever@redhat.com>
Acked-by: Mike Christie <mchristi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/target/target_core_user.c

@@ -2121,6 +2121,8 @@ static ssize_t tcmu_qfull_time_out_store(struct config_item *item,
 
 	if (val >= 0) {
 		udev->qfull_time_out = val * MSEC_PER_SEC;
+	} else if (val == -1) {
+		udev->qfull_time_out = val;
 	} else {
 		printk(KERN_ERR "Invalid qfull timeout value %d\n", val);
 		return -EINVAL;