net: cosa: fix error check return value of register_chrdev()

If major equal 0, register_chrdev() returns error code when it fails.
This function dynamically allocate a major and return its number on
success, so we should use "< 0" to check it instead of "!".
Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Lv Ruyi <lv.ruyi@zte.com.cn>
Acked-By: Jan "Yenya" Kasprzak <kas@fi.muni.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/wan/cosa.c

@@ -349,7 +349,7 @@ static int __init cosa_init(void)
 		}
 	} else {
 		cosa_major = register_chrdev(0, "cosa", &cosa_fops);
-		if (!cosa_major) {
+		if (cosa_major < 0) {
 			pr_warn("unable to register chardev\n");
 			err = -EIO;
 			goto out;